John Calvin on Numbers 25:3

3. AndIsrael joined himself to Baal-peor. Moses amplifies their crime by this expression, that they bound themselves to the idol in an impious alliance; and thus he alludes to that holy union whereby God had connected Himself with the people, and accuses them of broken faith and wicked rebellion. Nevertheless, it is probable that the people were not impelled by superstition, but enticed by the wiles of the women to offer worship to idols which they despised. Yet we are told how God declared that they were “joined” to the idol, which they merely pretended to worship, in order to comply with the ungodly wishes of the women. Hence, therefore, this general instruction may be gathered, that when we turn aside from pure religion, we in a manner connect ourselves with idols, so as to coalesce in one body with them, and conspire to renounce the true God.

Baal was then the general name of almost all idols; but all epithet is added to the idol of the Moabites, taken from Mount Peor; nor does it appear that we need go in quest of any other etymology, since the name of this mountain has recently been mentioned. It was on the same principle as in Popery, when they name their Marys after particular places, “Comme qui diroit nostre Dame de Laurette, ou de Boulogne, ou de Cleri;” as one might say, our Lady of Loretto, or Bologna, or Cleri. — Fr. where the most famous statues are worshipped.