Natural law is the reflection of God’s moral character and the moral order of creation, as designed by God, which is written on the human heart and evident through the light of nature (Rom. 2:14-15; Rom. 1:19; 1 Cor. 5:1), but held in unrighteousness (Rom. 1:18; Jer. 17:9; Prov. 14:12), whose substance is no different than the ten commandments. It is “the practical rule of moral duties to which men are bound by nature” (Turretin, Institutes, XI.i.5).
Therefore, the second commandment is written on the human conscience and can be known from the created order. It can be known from nature that we must worship God how he pleases rather than how we please (Acts 17:24-29), but we cannot know how God desires to be worshiped unless he reveals it to us through special revelation. Being the root of the second commandment, the Regulative Principle of Worship (RPW) itself is discernable from the light of nature as flowing from “that which may be known of God” (Rom. 1:19), while the parts and acts of God’s instituted worship is of divine positive law. 
“The law of nature teaches man to know that there is a God, and that this God is to be worshipped; whereupon it follows that man should seek to know God and the manner of his worship.” (George Gillespie, Dispute Against the English Popish Ceremonies, p. 362).
In this post we will look at John Calvin’s comments about this from Acts 17:24-29 and end with a few additional points demonstrating that the second commandment is revealed by the light of nature and written in man’s conscience.
Calvin on Acts 17:24-29
24 God that made the world and all things therein, seeing that he is Lord of heaven and earth, dwelleth not in temples made with hands; 25 Neither is worshipped with men’s hands, as though he needed any thing, seeing he giveth to all life, and breath, and all things; 26 And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation; 27 That they should seek the Lord, if haply they might feel after him, and find him, though he be not far from every one of us: 28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring. 29 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man’s device.
“24. God, who hath made the world. Paul’s drift is to teach what God is. Furthermore, because he hath to deal with profane men, he draweth proofs from nature itself…If any man will intreat generally of religion, this must be the first point, that there is some divine power or godhead which men ought to worship. But because that was out of question, Paul descendeth unto the second point, that true God must be distinguished from all vain inventions. So that he beginneth with the definition of God, that he may thence prove how he ought to be worshipped; because the one dependeth upon the other. For whence came so many false worshippings, and such rashness to increase the same oftentimes, save only because all men forged to themselves a God at their pleasure? And nothing is more easy than to corrupt the pure worship of God, when men esteem God after their sense and wit.
“Wherefore, there is nothing more fit to destroy all corrupt worshippings, than to make this beginning, and to show of what sort the nature of God is. Also our Savior Christ reasoneth thus, John 4:24, “God is a Spirit.” Therefore he alloweth no other worshippers but such as worship him spiritually…
“25. Neither is he worshipped with man’s hands. …Not only the philosophers, but also the poets, do sometimes deride the folly of the common people, because they did disorderly place the worship of God in the pomp and gorgeousness of ceremonies. That I may omit infinite testimonies, that of Persius is well known:
“Tell me, ye priests to sacred rites, what profit gold doth bring? The same which Venus’ puppets fine, certes [certainly] no other thing. Why give not we to gods that which the blear-eyed issue could of great Messiah never give from out their dish of gold? Right justly deem’d a conscience clear, and heavenly thoughts of mind, A breast with mildness such adorn’d, as virtue hath assign’d, Let me in temples offer these, Then sacrifice the gods shall please.” 
“And, undoubtedly, the Lord caused profane men to utter such speeches, that they might take away all color of ignorance. But it doth plainly appear, that those who spake thus did straightway slide back again unto common madness; yea, that they did never thoroughly understand what this meant…There is also a reason added, because, seeing he is Lord of heaven and earth, he needeth nothing, because, seeing that he giveth bread and life to men, he can receive nothing of them again. For what can they bring of their own, who, being destitute of all good things, have nothing but of his free goodness, yea, who are nothing but by his mere grace, who shall forthwith be brought to nought, if he withdraw the Spirit whereby they live? Whereupon it followeth, that they are not only dull, but too proud, if they thrust in themselves to worship God with the works of their own hands…
“27. That they might seek God. …Neither doth Paul intreat in this place of the ability of men, but he doth only show that they be without excuse, when as they be so blind in such clear light, as he saith in the first chapter to the Romans, (Romans 1:20)…
“Certain of your poets. He citeth half a verse out of Aratus, not so much for authority’s sake, as that he may make the men of Athens ashamed; for such sayings of the poets came from no other fountain save only from nature and common reason. Neither is it any marvel if Paul, who spake unto men who were infidels and ignorant of true godliness, do use the testimony of a poet, wherein was extant a confession of that knowledge which is naturally engraven in men’s minds…it is not to be doubted but that Aratus spake of Jupiter; neither doth Paul, in applying that unto the true God, which he spake unskillfully of his Jupiter, wrest it unto a contrary sense. For because men have naturally some perseverance of God (are imbued with some knowledge of God), they draw true principles from that fountain. And though so soon as they begin to think upon God, they vanish away in wicked inventions, and so pure seed doth degenerate into corruptions; yet the first general knowledge of God doth nevertheless remain still in them…
“29. Therefore seeing that. He gathereth that God cannot be figured or resembled by any graven image forasmuch as he would have his image extant in us. For the soul wherein the image of God is properly engraven cannot be painted; therefore it is a thing more absurd to go about to paint God. Now, we see what great injury they do to God which give him a bodily shape; when as man’s soul, which doth scarce resemble a small sparkle of the infinite glory of God, cannot be expressed in any bodily shape.
“Furthermore, forasmuch as it is certain that Paul doth in this place inveigh against the common superstition of all the Gentiles, because they would worship God under bodily shapes, we must hold this general doctrine that God is falsely and wickedly transfigured, and that his truth is turned into a lie so often as his Majesty is represented by any visible shape; as the same Paul teacheth in the first chapter to the Romans, (Romans 1:23). And though the idolaters of all times wanted not their cloaks and colors, yet that was not without cause always objected to them by the prophets which Paul doth now object that God is made like to wood, or stone or gold, when there is any image made to him of dead and corruptible matter. The Gentiles used images that, according to their rudeness, they might better conceive that God was nigh unto them. But seeing that God doth far surpass the capacity of our mind, whosoever attempteth with his mind to comprehend him, he deformeth and disfigureth his glory with a wicked and false imagination. Wherefore, it is wickedness to imagine anything of him according to our own sense. Again, that which worse is, it appeareth plainly that men erect pictures and images to God for no other cause, save only because they conceive some carnal thing of him, wherein he is blasphemed.
“The Papists also are at this day no whit more excusable. For what colors soever they invent to paint and color those images, whereby they go about to express God, yet because they be enwrapped in the same error, wherein the men of old time were entangled, they be urged with the of the prophets. And that the heathen did use the same excuses in times past, wherewith the Papists go about to cover themselves at this day, it is well known out of their own books. Therefore, the prophets do not escape the mocks of certain, as if they laid too great grossness to their charge, yea, burthen them with false accusations; but when all things are well weighed, those who will judge rightly shall find, that whatsoever starting holes [evasions] even the most witty men have sought, yet were they taken with this madness, that God is well pleased with the sacrifice done before images. Whereas we, with Erasmus, translate it numen, Luke putteth [theion] in the neuter gender for divinity or godhead. When Paul denieth that God is like to gold, or silver, or stone, and addeth afterward, graven by cunning or invention of man, he excludeth both matter and form, and doth also condemn all inventions of men, which disfigure the true nature of God.”
God is Spirit and Cannot Be Imaged
Ancient Greek philosopher Antiphanes wrote, “God is not discerned by an image, is not seen by the eyes, is like to no one, wherefore no one can learn him from an image” (De Deo).  Greek historian Plutarch records that Numa Pompilius (753–673 BC), king of Rome, criminalized graven images, which demonstrates that this moral principle is written in the conscience of men.
“Furthermore, his ordinances concerning images are altogether in harmony with the doctrines of Pythagoras. For that philosopher maintained that the first principle of being was beyond sense or feeling, was invisible and uncreated, and discernible only by the mind. And in like manner Numa forbade the Romans to revere an image of God which had the form of man or beast. Nor was there among them in this earlier time any painted or graven likeness of Deity, but while for the first hundred and seventy years they were continually building temples and establishing sacred shrines, they made no statues in bodily form for them, convinced that it was impious to liken higher things to lower, and that it was impossible to apprehend Deity except by the intellect.” (Plutarch, Lives of the Noble Greeks and Romans, p. 335. cf. Tertullian, Apology 25).
The ancient Greeks & Romans were not alone in their grasp of that which may be known of God from the light of nature. Heathen statesman and historian Publius Cornelius Tacitus (AD 56-120) records that Germanic pagans did not consider deity capable of being visually depicted.
“The Germans, however, do not consider it consistent with the grandeur of celestial beings to confine the gods within walls, or to liken them to the form of any human countenance. They consecrate woods and groves, and they apply the names of deities to the abstraction which they see only in spiritual worship.” (Germania, chapter 9).
Similarly, Herodotus (484-425 BC) records, “The Persians have neither statues nor altars, and think those who make them insane, because they do not (like the Greeks) think the gods to be the offspring of men” (The Histories, 1.131).
Pagans Understood the RPW
Heathen philosophers Socrates and Cicero understood from the light of nature that God must be approached on his own terms and that man should only worship God in the way he has prescribed, although they held the truth in unrighteousness (Rom. 1:18).
“Heathen Socrates and Cicero shall rise up against these pseudo-Christians [i.e. papists], and condemn them. God, said Socrates, will be worshipped with that kind of worship only which himself hath commanded. He will not be worshipped, said Cicero, with superstition, but with piety: Deus non superstitione coli vult sed pietate.” (John Trapp, Commentary on Matthew 15:9).
Additionally, the heathen sought special revelation regarding how the gods wanted to be worshiped, including song books of praise from their gods. Such as the Gathas of Zoroaster, the Samavedas of Hinduism, and the Norse Hávamál.
With the Law of God written upon their hearts, and not entirely destroyed by the Fall, even pagans, though suppressing the truth and redirecting their worship from the living God to created things (Rom. 1:18-24), have “some scintilla, some glimmerings, dawnings, and common principles of light, both touching piety to God, equity to man, and sobriety to a man’s self” (cf. Psalm 19:1-6, Acts 14:17, and 17:27-28; Rom. 1:18-21, and 2:12-15, 2 Cor. 5:1; Jus Divinum, p. 9). Yet these glimmerings are not sufficient for saving faith nor pure worship, but rather leave them all the more without excuse before God. “Reason out of nature teaches there is a God, but by the Word of God only do I believe it. Inducements to faith may be brought out of nature, but God’s Word only causes true belief.” 
Trapp’s point is worth meditating on. If even the heathen, who did not have the holy Scriptures, understood this principle of the second commandment, how much more judgment will be on those who have God’s Word, where it is faithfully and clearly expounded, and yet reject the RPW in principle and approach God in worship on their own terms rather than his? Surely “they are without excuse” (Rom. 1:20).
 cf. Natural Worship and Instituted Worship by William Ames.
 Persius, Satire II.
No doubt the following were a few of such pagan testimonies to which Calvin referred:
“The honour that is paid to the gods lies, not in the victims for sacrifice, though they be fat and glitter with gold, but in the upright and holy desire of the worshippers.” Seneca, De Beneficiis, p. 25.
“Precepts are commonly given as to how the gods should be worshipped…mortal ambitions are attracted by such ceremonies, but God is worshipped by those who truly know Him.” Seneca, Epistle 95.
 This is cited by Francis Turretin (IET XI.x.6) and Walter Charleton (Harmony of Natural and Positive Divine Laws, p. 128), but I am unable to find the exact source.
 William Perkins, Works 4.47. cf. Natural Idolatry by William Perkins.