John Calvin Commentary Psalms 106:37

"Yea, they sacrificed their sons and their daughters unto demons," — Psalms 106:37 (ASV)

And they sacrificed—the prophet here mentions one type of superstition that demonstrates the awful blindness of the people: their not hesitating to sacrifice their sons and daughters to devils. In applying such an abominable designation to the sin of the people, he means to portray it in a more detestable light.

From this we learn that misguided zeal is a flimsy pretext for any act of devotion. For the more the Jews were influenced by burning zeal, the more the prophet convicts them of greater wickedness, because their madness drove them to such an extreme of fanaticism that they did not spare even their own offspring.

If good intentions were meritorious, as idolaters suppose, then indeed, setting aside all natural affection in sacrificing their own children would have been a deed deserving the highest praise. But when people act from their own capricious impulses, the more they engage in acts of external worship, the more they increase their guilt.

For what difference was there between Abraham and those people whom the prophet mentions, except that the former, under the influence of faith, was ready to offer up his son, while the latter, carried away by intemperate zeal, cast off all natural affection and stained their hands with the blood of their own offspring?