Marrow of Sacred Divinity,
Book 2, ch. 5 § 1-8 & ch. 13
1. The parts of religion are two; natural worship, and voluntary or instituted worship.
2. This distinction is grounded on Exodus 20:6, those words of the second commandment: “who love me, and keep my commandments.”
3. Natural worship is that which depends upon the nature of God. So that although we had no Law revealed, and prescribed by God, yet if we did rightly perceive and know the nature of God, by a meet contemplation of it, we might, the grace of God helping us, perceive all those things which in this behalf pertains unto our duty. 
4. For there is nobody who understands the nature of God rightly, but withal he doth also necessarily acknowledge that God is to be believed and hoped in, that God is to be loved, called upon, and to be heard in all things.
5. Hence this natural worship is simply necessary to salvation (Ps. 79:6; Jer. 10:52; 2 Thes. 1:8). Power out thy wrath upon those nations that know thee not, and upon the kingdoms that call not upon thy name. For although we obtain eternal life neither by merit, nor by any virtue of our obedience, yet this part of obedience hath such an essential connection with that faith whereby we rest upon Christ to life eternal, that in exercise it cannot be separated from it.
6. Hence also this worship hath been, is, and shall be, one and the same, or immutable. “Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning” (1 John 2:7).
7. Natural worship is commanded in the first precept, not only as it is internal, but also as it is external.
8. For 1. All obedience is the same inwardly and outwardly, therefore the same inward and outward worship is contained in the same precept. 2. In those precepts which pertain to the second table, inward and outward obedience is together commanded in every one, Christ himself being interpreter (Mat. 5). Much more therefore in the precepts of the first table, and in the first and chief of them. 3. If that distinction were lawful, that the first precept would command only inward worship, and the second only outward, then the first commandment should bind the inward man, and the second only the outward man and the body, which is contrary to all reason.
. . .
1. Instituted worship is the means ordained by the will of God, to exercise and further natural worship.
2. All such like means ordained of God are declared in the second commandment, by forbidding all contrary means of worship devised by men, under the title of graven and image: which seeing they were of old the chief inventions of men corrupting the worship of God, they are most fitly (by a synecdoche frequent in the Decalogue) put instead of all devices of man’s wit pertaining to worship.
3. This worship does not depend in specie [in kind or form] and immediately upon the nature of God, or upon that honour which by virtue of our creation we owe to God, but upon the most free institution of God.
4. Hence this worship was diverse according to the diverse constitution of the Church; one before Christ exhibited, and another after.
5. It is a means having relation to the natural worship, otherwise it were not worship, because one cannot give that honour to God which is due to him, as touching the essence of the act, any other way than by faith, hope, and love, whereby we do receive from God with due subjection those things he propounds to us to be received, and with the same subjection we offer to him those things which may be offered by us to his honour. But because the acts themselves are in a special manner exercised in those things which God has instituted for his honour, therefore there is in them a certain secondary worship, and a certain partaking of the former.
6. But it has in respect to that natural worship  the affection of an effect, which exists by virtue of the former, and  of a means and instrument, whereby faith, hope, and love, (in which that worship is contained) do exercise their acts; and  of an adjuvant [helping; assisting] cause whereby they are furthered, and also  of an adjunct to which they are subjected.
Instituted Worship is a Means and Assistant to Natural Worship.
7. But it is properly called worship as it is a means and helping cause of that primary worship.
8. But because, the command of God being put, it depends and flows from the primary worship of God, therefore it is oft persuaded and urged by those arguments which are taken from the inward and essential manner of worshipping God, as in the second precept, “…them that love me and keep my commandments” (Ex. 20:6b). “What doth the Lord thy God require of thee, but to fear the Lord thy God, to walk in all his ways, and to love him, and to serve the Lord thy God with all thy heart and with all thy soul, to keep the commandments of the Lord, and his statutes…” (Deut. 10:12-13a).
9. That rule therefore of interpreting the Scripture which is wont to be delivered by some is not universally true, that all those duties [are] moral and immutable which have moral and immutable reasons joined to them; except it be thus understood, that those duties do follow upon those reasons, no special command coming between. “For I am the Lord your God: ye shall therefore sanctify yourselves, and ye shall be holy; for I am holy: neither shall ye defile yourselves with any manner of creeping thing that creepeth upon the earth” (Lev. 11:44).
10. No worship of this kind is lawful, unless it has God for the author, and ordainer of it. “Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the Lord your God which I command you” (Deut. 4:2). “What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it” (Deut. 12:32). “For because ye did it not at the first, the Lord our God made a breach upon us, for that we sought him not after the due order” (1 Chron. 15:13).
11. That is declared in those words of the commandment: “Thou shalt not make to thyself“—that is of thine own brain or judgement, for although that particle “to thyself” does sometimes either abound or has another force, yet here the most accurate brevity of these commandments does exclude redundancy, and it is manifest that the vanity of man’s cogitations is excluded by other places of Scripture pertaining to the same thing. As Amos 5:26 “…which ye made to yourselves” and Numbers 15:39 “…that ye seek not after your own heart and your own eyes, after which ye use to go a whoring.“
12. The same is also declared by that universality of the prohibition, which is explained in the commandment by a distribution of the things which are “in heaven above, or in the earth beneath, or in the water under the earth” (Ex. 20:4).
13. For none beside God himself can either understand what will be acceptable to him, or can add that virtue to any worship whereby it may be made effectual and profitable for us. Neither can there be anything honourable to God which comes not from him as the author of it. Neither finally do we read that such a power was at any time given to any man by God to ordain any worship at his own pleasure. “In vain do they worship me, teaching for doctrines the precepts of men” (Mat. 15:9).
14. Hence implicitly and by interpretation of God himself, we make him our God and give the honour due to God to him whose authority or ordinances we subject ourselves unto in religious worship.
15. In this respect also men are sometimes said to worship the Devil when they observe those worships which the Devil brought in (1 Cor. 10:20; Lev. 17:7; Deut. 32:17).
16. But we must observe that worship which God has appointed with the same religion, as we receive his word or will, or call upon his name (Deut. 6:17-18; 12:25, 28; 13:18; 28:14).
Elements of Worship and Church Government.
17. The means which God has ordained in this kind, some of them do properly and immediately make to the exercising and furthering of faith, hope, and charity—as public and solemn preaching of the word, celebration of baptism and the Lord’s Supper, and prayer. And some of them are means for the right performance of those former, as the combination of the faithful into certain congregations or churches, election, ordination, and ministration of ministers ordained by God, together with the care of ecclesiastical discipline.
18. Those former are most properly the instituted worship of God. Yet the rest are also worship, not only in that general respect as all things are said to be acts of worship and religion which do any way flow from, or are guided by, religion, but also in their special nature, because the adequate end and use of them is that God may be rightly worshipped.
19. All these therefore, both in general and in special, ought to be observed of us as they are appointed by God. For God must be worshipped by us with his own worship, totally and solely, nothing must here be added, taken away, or changed (Deut. 12:32).
20. That is a very empty distinction whereby some go about to excuse their additions: That only addition corrupting, and not addition conserving, is forbidden. Because every addition as well as detraction is expressly opposed to observation or conservation of the commands of God, as being a corruption (Deut. 12:32).
21. Of like stamp also is that evasion whereby they say there is forbidden only addition of essentials, and not of accidentals. For first although there be accidents or certain adjuncts of worship, yet there is no worship to be simply called accidental, because it has in it the very essence of worship. Secondly, as the least commands of God—even to iotas and tittles—are religiously to be observed (Mat. 5:18-19), so additions which seem very small are by the same reason to be rejected. Thirdly, Moses does seal up even those laws of the place of Divine worship, of the manner, of abstinence from blood, and the like, which must needs be referred to accidental worship (if any such be), with this very caution of not adding or taking away (Deut. 12:32).
Obedience, Will-worship, and Superstition.
22. This observation is in a special manner called obedience, because by it we do that which seems right in the eyes of the Lord, although some other may seem righter in our eyes (Deut. 12:25, 28).
23. There is opposed unto this instituted worship, as unlawful, that will-worship which is devised by men (Mat. 15:9; Col. 2:23).
24. The sin which is committed in will-worship is by a general name called superstition.
25. Superstition is that whereby undue worship is yielded to God.
26. For in superstition God is always the object, and the end in some measure, but the worship itself is unlawful.
Superstition: Manner or Measure vs. Matter and Substance.
27. It is called undue worship, either in respect of the manner or measure, or in respect of the matter and substance of the worship. In the former manner the Pharisees offended about the Sabbath when they urged the observation of it, as touching the outward rest, above the manner and measure appointed by God. And they also offended in the latter manner, in observing and urging their own traditions (Mark. 7:8).
28. Hence superstition is called an excess of religion, not in respect of the formal power of religion, because so none can be too religious, but in respect unto the acts and means of religion.
29. This excess is not only in those positive exercises, which consists in the use of things, but also in abstinence from the use of some things, as from meats, which are accounted unclean and unlawful, and the like.
30. Yet every abstinence, even from things lawful, although they be counted unlawful, is not superstition, to speak properly, unless there be some special worship and honour intended to God by that abstinence.
Acts of Worship and their Contrary Superstitions.
31. This undue worship is either properly opposed to that worship wherein instituted worship is directly put forth and exercised—that is, in hearing the word, celebration of the Sacraments, and prayer—or to that which respects the means of it.
Superstitions Opposed to the Hearing of the Word.
32. Unto the hearing of the word is opposed, first, a teaching by images devised by men (Deut. 4:15-16; Is. 40:18; Is. 41:29; Jer. 10:8, 15; Heb. 2:18). Secondly, a vaunting of traditions as they are propounded as rules of religion (Mat. 7:8).
33. Religious teaching by images is condemned: First, because they are not sanctified by God to that end. Secondly, because they can neither represent to us God himself, nor the perfections of God. Thirdly, because they debase the soul, and turn away the attention from spiritual contemplation of the will of God. Fourthly, because if they be once admitted into the exercises of worship, the worship itself by the perverseness of man’s wit, at least in part, will be transferred to them, as it is declared in those words of the commandment “Thou shalt not bow down to them, nor worship them.”
34. Of like kind with images are all those ceremonies which are ordained by men for mystical or religious signification.
35. For such ceremonies have no determinate power to teach either by any power put into them by nature, or by divine institution. But they can receive none by human institution because man can effect this neither by commanding, seeing it is beyond his authority, nor by obtaining, seeing God has promised no such thing to him that asketh.
36. Neither can men take to themselves any authority in ordaining such ceremonies, from that it is commanded to all churches that all things be done decently and in order (1 Cor. 14:40). For neither the respect of order nor decency requires that some holy things should be newly ordained, but that those which are ordained by God be used in that manner which is agreeable to their dignity. Neither do order and decency pertain to holy things only, but also to civil duties; for confusion and indecency in both are vices opposite to that due manner which is required to the attaining the just end and use of them.
Superstitions Opposed to the Sacraments.
37. To the Sacraments are opposed. (a) Sacrifices properly so called, whether they be bloody or unbloody, as the Papists fain of their Mass. For after Christ exhibited, all old sacrifices are abrogated. Neither is there any new ordinance, because the sacrifice of Christ being once offered we have no need of other types than those which pertain to the exhibition and sealing of Christ bestowed on us, which is sufficiently by God’s ordinance performed in the Sacraments (without sacrifices).
38. (b) Also the ordination and use of new seals or ceremonies sealing some grace of God is opposed to the Sacraments. For it belongs to him to seal grace to whom it belongs to give it.
Superstitions Opposed to Prayer.
39. Unto prayer is opposed that relative use of images whereby God is worshipped at them or before them, although the worship is not referred to the images themselves, as some say, subjectively, but objectively by [or through] them to God alone.
Idolatry of the 1st Commandment, and of the 2nd.
40. Superstition of this kind is called idolatry (Ex. 32:5; Ps. 106:20; Acts 7:41).
41. If they be idols which are in themselves worshipped instead of God, it is that idolatry which is against the First Commandment; but when the true God is worshipped at an image, or in an image, this is idolatry which is against the Second Commandment.
42. For although in respect of the intention of him that worships, he does not offend in the primary or highest object, yet from the nature of the thing itself he always offends against the formal worship of God. And interpretatively also a new god is feign for the object, who is delighted with such worship, and religious worship is given also to the image itself, although it be not done with that purpose that that worship be lastly bounded in the image, but that it be by that directed also to God himself.
43. Hence we must not only shun this idolatry as well as that absolute idolatry which is against the First Commandment, but also the very idols, and idolothites (or the things that are dedicated to idols), and all the monuments properly so called of idols (1 John 5:21; 1 Cor. 8:10; 1 Cor 10:18-19, 21; 2 Cor. 12:6, 26; Num. 33:52; Deut. 12:2-3; Exod. 23:13).
Superstition With Respect to Church Government.
44. Superstition of the second kind is in human forms of the Church, such as are churches that are visibly integrally, and organically, ecumenical, provincial, and diocesan, brought in by men. As also in the hierarchy agreeable to them, and orders of religious persons, who are found among the Papists, and in functions, and censures which are exercised by them.
45. The audaciousness of those men is intolerable who either omit the second commandment, or teach it ought to be so maimed that it should be read now under the New Testament: “Thou shalt not adore nor worship any likeness or image.”
 Cf. Samuel Willard, “[Natural worship] is to know God, to acknowledge him to be God, and glorify him as God. Now man, as a dependent creature, stands in need of help in this concern; much more fallen man, who has no natural light left in him, to direct him how to worship God acceptably. And therefore God has pleased to show him a way, wherein he may do it; and to this way belong all the institutions, appointed to man since the fall.” (Body of Divinity, Instituted Worship, Sermon CLIX).