The Israelites were engaging in licentious intercourse with the women of Moav and Midyan. This reached a nadir when Zimri, the prince of the tribe of Simeon, publicly consorted with a princess of Midyan. Pinhas was zealous on behalf of God and killed them. The Sages describe the contempt that Pinhas was subjected to by the people, and God’s reaction to his deed.

The tribes began to demean Pinhas: Did you see this son of Puti, [called such] because the father of his mother, Yitro, fattened [pitem] calves for idol worship, who killed the prince of a tribe of Israel? The verse comes and provides his lineage: “Pinhas son of Elazar son of Aaron the priest” (Numbers 25:11). The Holy One, Blessed be He, said to Moses: Be the first to greet Pinhas with a blessing of peace, as it is stated: “Therefore say: Behold I am giving him My covenant of peace” (25:12), and the atonement [engendered by the act of Pinhas] is worthy of continuing to atone forever. (Sanhedrin 82a)