Or HaChaim on Numbers 25:12/אור החיים על במדבר כ״ה:י״ב

1 לכן אמור, "Therefore, 'say,'" etc. Why did the Torah have to write the word לכן, "Therefore," seeing it goes on to explain in verse 13 "because he was jealous for his G'd?" We are forced to understand the word as an oath. We have learned in Shemot Rabbah 6,4 on Exodus 6,6 that this word is always to be understood as a form of oath. The Midrash uses as its source Samuel I 3,14, ולכן נשבעתי לבית עלי, "And this is why I have sworn an oath concerning the house of Eli, etc." This still leaves us with the question why an oath was required in this instance. Presumably, the oath was needed to reinforce the covenant of peace in the event that Pinchas' children should turn out not to be deserving of the covenant G'd had concluded with their father.

2We may also be able to explain this verse on the basis of what we learned in Zevachim 101 that prior to the incident with Zimri Pinchas had not yet been appointed to the priesthood, as, although he was around at the time Aaron and his sons were anointed, he himself had not bothered to be anointed. After he performed his deed of jealousy on behalf of G'd he was appointed to the priesthood. Pinchas could have acquired the priesthood either as an act of forgiveness or as a gift from G'd. In the former event, his deed prompted G'd to forgive him for having failed at the time to have himself anointed. If we see in his appointment now a gift from G'd, we may view it as something entirely new. Just as Aaron and his sons were appointed to be priests, though Amram Aaron's father and his brothers had not been priests, so Pinchas' appointment was something quite new. There is a halachic difference between priesthood acquired as an act of forgiveness and priesthood acquired as a gift. In the fomer case, the priest need not perform an act of קנין, a symbolic act of acquisition of the priesthood; however, someone who had not had a previous claim to the priesthood and was awarded same as a gift must perform such an act of קנין.

3Receiving the priesthood as a gift carries with it two disadvantages which the person who receives the priesthood as an act of forgiveness need not worry about. If the priesthood was attained via G'd forgiving Pinchas for an act of negligence in the past, then, if Pinchas were to be appointed High Priest at a future date he would not have to face any challengers. Any challenge would be dealt with as had the challenges against Aaron becoming High Priest. If the priesthood were to be granted only as a gift, the priest in question could face challenges to his promotion just as did Aaron before G'd had intervened. Such a challenge would be reinforced by the fact that Pinchas had killed. A priest who has killed is supposedly unfit to perform his priestly duties. People would claim that inasmuch as the status of the priesthood granted as a gift is limited to the recipient of that gift becoming an ordinary priest, such a priest does not qualify to compete for the office of High Priest. This is not so when a potential priest regains his former status through the act of G'd's forgiveness. Seeing that he had been in line for the office of High Priest before he had forfeited it through negligence, G'd's forgiveness reinstates such a potential priest in his former status. As a result of these considerations, obtaining the priesthood by way of an act of forgiveness from G'd is superior in three ways to obtaining it as a mere gift. 1) No formal act of acquisition is needed. 2) One need not worry about potential challengers to one's promotion. 3) It is an enduring status transferable to one's children and grandchildren as something hereditary.

4In His wisdom, G'd decided to accord Pinchas the priesthood as a gift in order to demonstrate that he did not become a priest merely through a hereditary claim to the priesthood instead of a claim based on moral excellence. By appointing Pinchas as priest directly, G'd elevated the meaning of Pinchas' priesthood, made it into something which he could point to as a mark of personal distinction. This is why the Torah describes G'd as saying: "Here I give to him My covenant, peace." In view of our having pointed out that such a gift by definition may not be transferable to one's children, G'd had to reinforce the gift by an oath, i.e. the word אכן, in order to make the appointment as enduring as if it had been acquired through an act of forgiveness. This is why G'd had to add לו ולזרעו אחריו "to him and his descendants after him." The "peace" included that no one would challenge Pinchas' claim to the priesthood and the office of High Priest when the time came. I have pointed out on a previous occasion that the word כהונה is the name of a certain category of souls known as such in the region where the souls are at home. G'd assured Pinchas that his descendants would always receive souls drawn from the pool of souls known as כהונה. This is the mystical dimension of the expression כהונת עולם.