Or HaChaim on Numbers 25:13/אור החיים על במדבר כ״ה:י״ג

1 תחת אשר קנא לאלוקיו, because he displayed jealousy on behalf of His G'd. This verse provides the reason why G'd decided to give the priesthood to Pinchas as a gift rather than in his capacity of being the son of a priest. By pointing out that what Pinchas had done, he did on account of his G'd, G'd repaid him by elevating him to the priesthood as an act of honouring him personally. He did this by demonstrating that Pinchas did not have to rely on his ancestry, i.e his father and grandfather the High Priests in order to become a priest himself. ויכפר על בני ישראל, he atoned on behalf of the children of Israel. This means that he re-established peace between Israel and their Father in Heaven that G'd in turn called off the angel of death. Inasmuch as Pinchas had caused G'd to call off the angel of death from his people, his people made a pact of peace with him. Inasmuch as the benefits the Israelites derived from Pinchas' calling off the angel of death from them, in other words a benefit extending from generation to generation, Pinchas' elevation to the priesthood was also one that extended from generation to generation, i.e. כהונת עולם.

2A moral/ethical approach to our verse could be based on the statement in Baba Metzia 114, that the prophet Elijah who would usher in the messianic age would be none other than Pinchas (his re-incarnation). Our verse would provide the reason why it would be Pinchas who would perform this task in the future. We are told that the principal function of the prophet Elijah at the time preceding the arrival of the Messiah will be to bridge the generation gap between fathers and sons and vice-versa, harmonising their mutual relationships (compare Maleachi 3,24). In addition to that we have learned in Edioth 8,7 that Elijah would increase שלום, harmony in the world. You will observe that in our paragraph the Torah describes Pinchas twice as being jealous, once in verse 11 and once more in our verse here. The Torah alludes to the jealousy the original Pinchas displayed on G'd's behalf during the time the Israelites were at Shittim, whereas the second reference is to the jealousy the prophet Elijah (Pinchas) displayed during the reign of King Achav when he described himself before G'd as a Kannai, a fanatic on G'd's behalf (Kings I 19,14). There too we find that he repeated the word קנא, "was jealous." At that time, Elijah alluded to the fact that this was already the second time he had played this role of being jealous on behalf of G'd. The Torah therefore mentions here that G'd granted him G'd's covenant of peace.

3What is the meaning of that covenant? The word שלום is to be understood as "complete, whole." The first covenant G'd concluded with the first Jew Abraham in Genesis 15, 1-21 contained the promise that Abraham's descendants would take possession of the lands of 10 nations all of which are named in that chapter. Even at the time when the prophet Elijah was active on earth for the first time, the lands of no more than seven of these nations had been given to the Jewish people. When G'd said in our verse הנני נותן לו את בריתי שלום, He hinted that Pinchas/Elijah would preside over the completion of the part of G'd's promise to Abraham which was still outstanding. The vision of Maleachi includes the vision of Isaiah 11,7 and 9 concerning a period when the lion will lie down with the lamb without harming it, etc. In the latter verse Isaiah predicts that from that time onwards "nothing evil or vile shall be done, for the land will be filled with devotion to the Lord, etc. etc."The reason that in our verse G'd does no longer speak of Pinchas' descendants is that when Elijah will return at that time it will be Pinchas' final appearance on earth, his task will not have to be completed by his offspring. The Torah mentions that the covenant G'd concludes with Pinchas also comprises the priesthood, giving a reason for this second covenant which is an everlasting one. By using the introductory word תחת, the Torah refers to Pinchas as also qualifying for this latter covenant on account of two things he had done or was still going to do, i.e. the jealousy he would display on behalf of G'd during the reign of Achav when the Israelites worshiped the Baal and abandoned their G'd. The reason that the Torah added the word לאלקיו here is that it alludes to the sin of idol worship. We know from Deut. 6,15 that the sin of idol worship arouses G'd's jealousy. When Elijah demonstrated the miracles of G'd on Mount Carmel in Kings I 18,39, he did not conclude until the people had exclaimed that the Lord G'd is the true G'd. This is the reason why when Elijah will appear once more prior to the coming of the Messiah it will be during a period which the prophet Maleachi described as a time when "G'd and His name will be one," the mystical dimension of "the Lord G'd is the true G'd."

4The word ויכפר, etc. also refers both to the future and to the past. The Torah means that just as Pinchas had atoned for the Jewish people in Shittim, so Elijah would atone for the Jewish people in the future. Basically, this is the function of the priest, as we know from Leviticus 4,20 et al.