John Calvin Commentary Isaiah 57:5

"ye that inflame yourselves among the oaks, under every green tree; that slay the children in the valleys, under the clefts of the rocks?" — Isaiah 57:5 (ASV)

Inflaming yourselves. Others translate it as “Taking delight” or “consolation;” but the Prophet uses a metaphor that is often found in Scripture and is exceedingly well-suited to the present subject. For the Lord compares the ardor by which idolaters are hurried along to the love of a harlot, by which poor, wretched men are inflamed so as to be transported with blind eagerness (Jeremiah 3:1; Hosea 2:2; Hosea 4:5). Idolaters have no moderation and do not permit themselves to be reclaimed from their madness by any arguments. In the sight of God, idolatry is a very base kind of fornication.

Under the oaks, or, with the gods. Some translate אלים (elim) as “gods,” and others as “oaks.” I leave everyone free to adopt either reading, for the meaning will always be the same, and commentators agree that the Prophet condemns idolatry. Therefore, I do not dispute the reading. It is probable, however, that the same thing is repeated twice, in accordance with the practice of Hebrew writers—in a particular and then in a general form—and that the Prophet, by means of an ambiguous word, also alludes to “the gods.”

Sacrificing children. Here he presses even harder on the Jews and shows that they are not the true seed of Abraham, since they pollute themselves with superstitions of every kind. Because of the delight the Jews took in such practices, he exposes their vileness: “You shelter yourselves, indeed, under the name of religion, but I declare that you commit fornication with idols.” In this way, it was proper to expose and freely point out the wickedness that base and malicious men try to cloak with various pretenses. Thus, the Prophet boldly discharges his duty by summoning people to the judgment seat of God and holding them guilty, even though they try every method to excuse themselves.

He shows that they are treacherous and have departed from the law of God by abominable idolatry, and he mentions one kind of shocking, even accursed and monstrous worship: namely, the “sacrificing of children.” From this, it is very evident how powerful the spirit of error is once people have turned aside from God. Satan seizes their minds (2 Thessalonians 2:9) in such a way that he drives them completely into madness and rage. Those who do not hesitate to kill their children, as if it were a righteous sacrifice, must be in a state of furious madness.

And yet those cruel murderers of their children did not lack some pretense, for they cloaked their crime with the example of Abraham, who did not spare (Genesis 22:16) his only-begotten son. The ancient Hebrew writers pronounce it to have been (κακοζηλία) a wicked imitation: “If we are Abraham’s descendants, we ought not to spare our children.” But Abraham did this (Genesis 22:2) by the command of God, while they did it of their own accord and without God’s command.

It was an extraordinary example by which the Lord intended to test and attest Abraham’s faith. Besides, Isaac was not sacrificed, for the Lord was satisfied with Abraham’s cheerful and ready will (Genesis 22:12). They killed their children. It was, therefore, a perverse and damnable imitation, for they differed widely from their father. This should be carefully observed, for a large portion of superstitions has proceeded from this source of (κακοζηλία) wicked imitation. People have rashly and without discrimination seized on everything that was done by the fathers.