1 And Israel abode in Shittim, and the people began to commit whoredom with the daughters of Moab. 2 And they called the people unto the sacrifices of their gods: and the people did eat, and bowed down to their gods. 3 And Israel joined himself unto Baal-peor: and the anger of the LORD was kindled against Israel. 4 And the LORD said unto Moses, Take all the heads of the people, and hang them up before the LORD against the sun, that the fierce anger of the LORD may be turned away from Israel. 5 And Moses said unto the judges of Israel, Slay ye every one his men that were joined unto Baal-peor. 6 And, behold, one of the children of Israel came and brought unto his brethren a Midianitish woman in the sight of Moses, and in the sight of all the congregation of the children of Israel, who were weeping before the door of the tabernacle of the congregation. 7 And when Phinehas, the son of Eleazar, the son of Aaron the priest, saw it, he rose up from among the congregation, and took a javelin in his hand; 8 And he went after the man of Israel into the tent, and thrust both of them through, the man of Israel, and the woman through her belly. So the plague was stayed from the children of Israel. 9 And those that died in the plague were twenty and four thousand. 10 And the LORD spake unto Moses, saying, 11 Phinehas, the son of Eleazar, the son of Aaron the priest, hath turned my wrath away from the children of Israel, while he was zealous for my sake among them, that I consumed not the children of Israel in my jealousy. 12 Wherefore say, Behold, I give unto him my covenant of peace: 13 And he shall have it, and his seed after him, even the covenant of an everlasting priesthood; because he was zealous for his God, and made an atonement for the children of Israel. 14 Now the name of the Israelite that was slain, even that was slain with the Midianitish woman, was Zimri, the son of Salu, a prince of a chief house among the Simeonites. 15 And the name of the Midianitish woman that was slain was Cozbi, the daughter of Zur; he was head over a people, and of a chief house in Midian. 16 And the LORD spake unto Moses, saying, 17 Vex the Midianites, and smite them: 18 For they vex you with their wiles, wherewith they have beguiled you in the matter of Peor, and in the matter of Cozbi, the daughter of a prince of Midian, their sister, which was slain in the day of the plague for Peor's sake.
[AD 253] Origen of Alexandria on Numbers 25:2
I might say that those who deny Christianity on oath at the tribunals or before they have been put on trial do not worship but only bow down to idols when they take “God” from the name of the Lord God and apply it to vain and lifeless wood. Thus the people who were defiled with the daughters of Moab bowed down to idols but did not worship them. Indeed, it is written in the text itself, “They invited them to the sacrifices of their idols, and the people ate of their sacrifices, and they bowed down to their idols, and performed the rites to Baal Peor.” Observe that it does not say “and they worshiped their idols”; for it was not possible after such great signs and wonders in one moment of time to be persuaded by the women with whom they committed fornication to consider the idols gods.

[AD 1781] Richard Challoner on Numbers 25:3
Initiated to Beelphegor: That is, they took to the worship of Beelphegor, an obscene idol of the Moabites, and were consecrated, as it were, to him.
[AD 386] Cyril of Jerusalem on Numbers 25:8
If Phinehas by his zeal in slaying the evildoer appeased the wrath of God, shall not Jesus, who slew no other but “gave himself a ransom for all,” take away God’s wrath against humanity?

[AD 395] Gregory of Nyssa on Numbers 25:8
Now if we have been conformed to his death, sin henceforth in us is surely a corpse, pierced through by the javelin of baptism, as that fornicator was thrust through by the zealous Phinehas.

[AD 407] John Chrysostom on Numbers 25:8
Slaughter has brought about righteousness, and mercy has been a cause of condemnation more than slaughter, because the latter has been according to the mind of God, but the former has been forbidden. It was reckoned to Phinehas for righteousness that he pierced to death the woman who committed fornication, together with the fornicator. But Samuel, that saint of God, although he wept and mourned and entreated for whole nights, could not rescue Saul from the condemnation which God issued against him, because he saved, contrary to the design of God, the king of the alien tribes whom he ought to have slain.

[AD 220] Tertullian on Numbers 25:9
As far as that goes, we too have examples from this same past in favor of our own way of thinking, examples of a judgment on fornication which was not only not remiss but rather immediately executed. It is quite enough, I should think, that so great a number of the chosen people, twenty-four thousand, perished at one stroke after they had fornicated with the daughters of Midian. I prefer, however, for the glory of Christ, to derive ecclesiastical discipline from Christ.

[AD 253] Origen of Alexandria on Numbers 25:10
And lest we appear to you to bring these things forth from our own understanding rather than from the authority of the divine Scriptures, go back to the book of Numbers and recall what Phinehas the priest did when he saw a harlot of the Midianite people with an Israelite man clinging in impure embraces in the eyes of all. Filled with the wrath of divine jealousy, he drove a sword, which he had seized, through the breast of both. This work was imputed to him by God for righteousness when the Lord says, “Phinehas appeased my rage, and it shall be imputed to him for righteousness.” That earthly food of anger therefore becomes our food when we use it rationally for righteousness.

[AD 397] Ambrose of Milan on Numbers 25:13
God is neither unjust nor is his judgment changeable. For God laid hold of [Balaam’s] mind and the secrets of his heart. For that reason he tested him as a diviner; he did not elect him as a prophet. And certainly he ought to have been converted by the grace of such great oracles and the sublimity of the revelations. But his soul, full of vileness, put forth words, but it did not bring forth faith. He desired to undermine by his counsel what he announced would happen. Since he was not able to give the lie to the oracles, he proposed fraudulent counsels. By these counsels the fickle people of Israel were indeed tested, but they were not overcome. For by the justice of one man, a priest, every plan of that villainous man was undone. It is much more amazing that the multitude of our fathers could be freed through one man than be deceived through one man.