Matthew Poole and continuators on Numbers 25:13

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.

Quest. What advantage had he by this promise, seeing the thing here promised was due to him by birth? Answ. 1. The same blessing may be oft-times promised, as the Kingdom was to David; and the renewing of this promise might feem convenient here, to signifie that bloodshed was so far from polluting him and thereby casting him out of the Priesthood, that it was a mean to confirm him in it. 2. This promise secured him and his against divers contingences, which otherwise have been befallen him or them, as that he should live longer than his father, else he could not have been the High-priest; that he should be preserved from those blemishes which might have rendred him uncapable of the Priesthood, which were many; that he should have a seed and they such as were fit for that office.

(i. e.) To continue as long as the Law and Commonwealth of the Jews did. Quest. How was this verified, seeing the Priesthood went from Eleazars to Ithamars line in Eli and three or four of his Successours? Answ. 1. This promise, as others of the like nature, was conditional, and therefore might be made void and of none effect by the miscarriages of Phinehas his sons, as it seems it was, and thereupon a like promise was made to Eli of the line of Ithamar, that he and his should walk before the Lord, to wit, in the office of High-Priest, for ever, which also for his and their sins was made void, 1 Sam. 2. 30. Answ. 2. That was but a short interruption, and not considerable in so long a succession, for the Priesthood returned to Phinehas his line in the time of Solomon, 1 King. 2. 26, 27, 34. 1 Chron. 24. 3. and continued in that line till the captivity of Babylon, as is evident, and afterward too, 1 Chron. 6. 4. Ezra 7. 1, 5. even untill Christs time, for any thing which appears to the contrary.