John Calvin Commentary Numbers 25:3

"And Israel joined himself unto Baal-peor: and the anger of Jehovah was kindled against Israel." — Numbers 25:3 (ASV)

And Israel joined himself to Baal-peor. Moses amplifies their crime with this expression, stating that they bound themselves to the idol in an impious alliance; and thus he alludes to that holy union by which 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 driven by superstition but were enticed by the deceptions of the women to offer worship to idols they despised. Yet we are told how God declared that they were “joined” to the idol, which they merely pretended to worship to comply with the ungodly wishes of the women.

Therefore, this general instruction may be gathered: when we turn aside from pure religion, we, in a manner, connect ourselves with idols, so as to coalesce into one body with them and conspire to renounce the true God.

Baal was then the general name of almost all idols, but an epithet is added to the idol of the Moabites, taken from Mount Peor. Nor does it appear that we need to search for 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,¹⁸³ where the most famous statues are worshipped.

¹⁸³ “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.