And Israel {b} joined himself unto Baalpeor: and the anger of the LORD was kindled against Israel.

(b) Worshipped the idol of the Moabites, which was in the hill Peor.

Wesley's Notes

25:3 Joined himself - The word implies a forsaking God to whom they were joined and a turning to, and strict conjunction with, this false God. Baal - peor - Called Baal, by the name common to many false Gods, and especially to those that represented any of the heavenly bodies, and Peor, either from the hill Peor, where he was worshipped, Num 23:28, rather from a verb signifying to open and uncover, because of the obscene posture in which the idol was set, as Priapus was: or because of the filthiness which was exercised in his worship.

Scofield Reference Notes

Margin Baal-peor

Or, Baal of Peor. See Num 23:28.

Jamieson-Fausset-Brown Bible Commentary

3. Israel joined himself unto Baal-peor-Baal was a general name for "lord," and Peor for a "mount" in Moab. The real name of the idol was Chemosh, and his rites of worship were celebrated by the grossest obscenity. In participating in this festival, then, the Israelites committed the double offense of idolatry and licentiousness.

Matthew Henry's Concise Commentary

25:1-5 The friendship of the wicked is more dangerous than their enmity; for none can prevail against God's people if they are not overcome by their inbred lusts; nor can any enchantment hurt them, but the enticements of worldly interests and pleasures. Here is the sin of Israel, to which they are enticed by the daughters of Moab and Midian. Those are our worst enemies who draw us to sin, for that is the greatest mischief any man can do us. Israel's sin did that which all Balaam's enchantments could not do; it set God against them. Diseases are the fruits of God's anger, and the just punishments of prevailing sins; one infection follows the other. Ringleaders in sin ought to be made examples of justice.