John Calvin Commentary Isaiah 57:8

"And behind the doors and the posts hast thou set up thy memorial: for thou hast uncovered [thyself] to another than me, and art gone up; thou hast enlarged thy bed, and made thee a covenant with them: thou lovedst their bed where thou sawest it." — Isaiah 57:8 (ASV)

Behind the door. He elaborates extensively on the crime of which we have already spoken, so that the people may no longer flatter themselves with their human contrivances. It is probable that Isaiah alludes to the words of Moses, by which God commanded them to have the Law continually placed before them, to attach it to the posts of their houses, and to keep it written and wrapped around their arms and the fringes of their garments, so that they might be constantly reminded of their duty (Deuteronomy 6:9, 11:20). But the Jews, on the contrary, polluted the doors and posts of their houses with tokens of idolatry, and left no corner free or pure from such pollutions. Thus they came everywhere to forget God and the Law, and substituted in their place the allurements of their own lust.

You have enlarged your bed. He again repeats what he previously said, and returns to the point that the Jews most shamefully commit fornication with idols when they think they are worshipping God, because they do not follow the rule of the word. It is as if a woman, having forsaken her husband, were to prostitute herself in a brothel and freely receive all who came, as if the bed were a large plain, able to hold a vast multitude.

For this reason, he says that she was exposed by him. Because, having abandoned the modesty proper to marriage, she allowed herself to be dishonored and violated by others. For God holds the place of a husband, to whom she should have been subject; but she sought new husbands and broke the bond of marriage. He describes their aggravated guilt by saying that the Jews, of their own accord, devoted themselves to idols, just as an immoral woman might pursue a man with blind eagerness.

You loved their bed in the place which you saw. By a different figure of speech, he accuses them of that hasty love, because, as if by a single glance, they were suddenly and eagerly drawn to any place whatsoever. Yet he blames the rashness of people who think they are wise in worshipping God and select places according to their own pleasure. But this supposed wisdom is diabolical, for God commands us to keep our eyes fixed on Him and His word, so that they remain closed to everything else.