My covenant of peace - of an everlasting priesthood - As the word peace implied all kinds of blessings, both spiritual and temporal, it may mean no more here than the promise of God, to grant him and his family the utmost prosperity in reference to both worlds. The everlasting priesthood refers properly to the priesthood of Christ which was shadowed out by the priesthood under the law; no matter in what family it was continued. Therefore the כהנת עולם kehunnath olam, or eternal priesthood, does not merely refer to any sacerdotal ministrations which should be continued in the family of Phinehas, during the Mosaic dispensation, but to that priesthood of Christ typified by that of Aaron and his successors. The priesthood alone is everlasting, and a covenant or grant of that was made to Phinehas, and his descendants. The Jews reckon twelve high priests of the race of Phinehas, from this time to the days of Solomon, nine more from that time to the captivity, (see 1 Chronicles 6:4, 1 Chronicles 6:15), and fifteen from their return to the time of Antiochus Eupator, the last of whom was Onias, slain by Lysias. Ezra, the great priest and scribe, was of this line, Ezra 7:1, Ezra 7:5. The family of Ithamar, uncle of Phinehas, had the priesthood for about 150 years; but it was restored to the family of Phinehas in the person of Zadok the priest, 1 Chronicles 6:50, in which it continued in the whole about 950 years. Probably the Maccabees were of the same family; but though this is not certain, there is no evidence against it. See Calmet. God therefore sufficiently fulfilled his promise; he gave to him and his descendants almost the utmost temporal length that could be given of that priesthood which is, in its own nature, eternal. Here then the word עולם olam means, not a limited time, but what is eternal in its duration. See the note on Genesis 21:33.

a prince

Numbers 25:4,5 And the LORD said to Moses, Take all the heads of the people, and hang them up before the LORD against the sun...

2 Chronicles 19:7 Why now let the fear of the LORD be on you; take heed and do it: for there is no iniquity with the LORD our God, nor respect of persons...

chief house. Heb. house of a father. the Simeonites

Numbers 1:23 Those that were numbered of them, even of the tribe of Simeon, were fifty and nine thousand and three hundred.

Numbers 26:14 These are the families of the Simeonites, twenty and two thousand and two hundred.

How those that are at Variance and those that are at Peace are to be Admonished.
(Admonition 23.) Differently to be admonished are those that are at variance and those that are at peace. For those that are at variance are to be admonished to know most certainly that, in whatever virtues they may abound, they can by no means become spiritual if they neglect becoming united to their neighbours by concord. For it is written, But the fruit of the Spirit is love, joy, peace (Gal. v. 22). He then that has no care to keep peace refuses to bear the fruit of the Spirit. Hence Paul …
Leo the Great—Writings of Leo the Great