• Pinchas would have been killed for killing Zimri after the act, and Zimri could have killed Pinchas

Rav Chisda said: הבא לימלך – if one asks Beis Din if he should kill someone having relations with a gentile woman, אין מורין לו – [they] do not instruct him to do so, because the law of קנאין פוגעין בו only applies to one who acts one his own. Rebbe Yochanan said the same, and added שאם פירש זמרי והרגו פנחס – if Zimri had separated himself from Cozbi and Pinchas would have killed him after, נהרג עליו – [Pinchas] would have been executed for it, because the permit to kill someone having relations with a gentile woman is only while the act is being committed. Finally, נהפך זמרי והרגו לפנחס – if Zimri would have turned around and killed Pinchas, אין נהרג עליו – he would not have been executed for it, שהרי רודף הוא – because Pinchas was considered a “pursuer” (although it was permitted for Pinchas to kill him), so Zimri could save himself even by killing Pinchas.

• What Pinchas “saw” that caused him to act – one opinion: אין חכמה ואין תבונה ואין עצה לנגד ה'

The Gemara relates that Zimri approached Cozbi for relations, and dragged her by her hair to Moshe, and challenged Moshe that if she was forbidden to him, בת יתרו מי התירה לך – “Who permitted Yisro’s daughter to you?” The law of קנאין פוגעין בו was hidden from Moshe at that time, and everyone began weeping. The passuk says that Pinchas “saw,” and the Gemara asks what it was. Rav says: ראה מעשה ונזכר הלכה – he saw the incident and remembered the halachah. He said to Moshe, did you not teach about one who has relations with a Kusis, קנאין פוגעין בו? Moshe replied: קריינא דאיגרתא איהו ליהוי פרוונקא – the reader of the letter should be the agent to follow its instructions. Shmuel says Pinchas “saw” the passuk, "אין חכמה ואין תבונה ואין עצה לנגד ה'" – there is no wisdom or understanding or counsel against Hashem’s honor, teaching: כל מקום שיש חילול השם אין חולקין כבוד לרב – wherever there is desecration of Hashem’s Name, we are not concerned with giving honor to a teacher, so he acted without consulting Moshe, his teacher. Rebbe Elazar says he “saw” a מלאך destroying the nation and acted immediately.

•  Pinchas’s killing Zimri, six miracles, and Hashem’s defense of Pinchas

The Gemara relates that Pinchas hid the spear tip in his garment and approached the shevet of Shimon using the spear as a “walking stick,” and implied that he sought to join the sinning, allowing him access to Zimri’s tent. The Gemara relates six miracles performed for Pinchas on that day, enabling him to kill Zimri, and to publicly demonstrate what Zimri was doing. Pinchas threw down their bodies before Hashem and said, “Ribbono Shel Olam! Because of these, twenty-four thousand people of Yisroel should die?!” The passuk says "ויפלל" – and [Pinchas] prayed, instead of "ויתפלל", and Rebbe Elazar explains: כביכול שעשה פלילות עם קונו – that he made a quarrel, as it were, with his Creator. The מלאכי השרת wanted to push him away, but Hashem said: הניחו לו קנאי בן קנאי הוא – Leave him, he is a zealot, the son of a zealot (i.e., Levi, in avenging Dinah’s disgrace); משיב חימה בן משיב חימה הוא – he is one who turns back anger, the son of one who turned back anger (i.e., Aharon, who ended the plague in the incident of Korach). The shevatim began mocking Pinchas, saying he was a descendant of Yisro, who fattened calves for avaodah zarah, so the Torah identifies him as a descendant of Aharon. Hashem told Moshe: הקדם לו שלום – be first to greet him in peace, based on a passuk.