In preaching through the prophet Zephaniah this Advent season, I have been edified in reading Calvin's commentaries on the prophet. This is Calvin at his best, following his typical pattern of exposition and then application.

In commenting on Zephaniah 1:5 and 1:6, he applies the text in terms of worshipping God as he commands in his word and not how we want to worship him—with obvious veiled references to Rome of his day.

On 1:5, And them that worship the host of heaven upon the housetops; and them that worship and that swear by the LORD, and that swear by Malcham, he says,

What then was it that the Prophet condemned that they were not content with what the law simply and plainly prescribed, but that they devised for themselves various and strange modes of worship; for when men take to themselves such a liberty as this, they no longer worship the true God, how much soever they may pretend to do so, inasmuch as God repudiates all spurious modes of worship, as he testifies especially in Ezekiel 20 — Go ye, he says, worship your idols. He shows that all kinds of worship are abominable to him whenever men depart in any measure from his pure word. For we must hold this as the main principle — that obedience is more valued by God than all sacrifices. Whenever men run after their own inventions they depart from the true God; for they refuse to render to him what he principally requires, even obedience (Emphasis added).

On 1:6, And them that are turned back from the LORD; and those that have not sought the LORD, nor enquired for him, he says,

Nor was it to be wondered at, that so grievous and severe a sentence was pronounced on them; for they had been taught by the law how God was to be served. How was it, then, that errors so gross had crept in? Doubtless, God had kindled the light of celestial truth, which clearly showed the way of true religion; but as men ever seek to perform some frivolous trifles, the Israelites and the Jews, when they felt ashamed openly and manifestly to reject the true God, labored at the same time to add many ceremonies, that their impiety might be thus concealed. This is the reason why the Prophet says that they turned back; that is, that they could not be excused on the ground of ignorance, but that they were perfidious and apostates, who had preferred their own idols to the true God; though they knew that he could not be rightly worshipped, but according to the rule prescribed in the law, they yet neglected this, and heaped together many superstitions. And, doubtless, we shall find that the fountain of all false worship is this — that men are unwilling truly and from the heart to serve God; and, at the same time, they wish to retain some appearance of religion. For there is nothing omitted in the law that is needful for the perfect worship of God: but as God requires in the law a spiritual worship, hence it is that men seek hiding-places, and devise for themselves many ceremonies, that they may turn back from God, and yet pretend that they come to him. While they sedulously labor in their own ceremonies, it is indeed true that the worship of God and religion are continually on their lips: but, as I have said, it is all hypocrisy and deception; for they accumulate ceremonies, that there might be something intervening between God and them. It is not, therefore, without reason that the Prophet here accuses the Jews that they turned back from Jehovah, and that they sought him not. How so? For there was no need of a long, or of a difficult, or of a perplexed enquiry; for the Lord had freely offered himself to them. How, then, was it that they were blind in the midst of light, except that they knowingly and willfully followed their own inventions? The same is the case at this day with the Papists: for though they may glamour a hundred times that they seek to worship God, it is quite evident that they willfully go astray; inasmuch as they so delight themselves with their own inventions, that they do not purely and from the heart devote and consecrate themselves to God.