And Benaiah the son of Jehoiada was over the host: and Zadok and Abiathar were the priests:
Benaiah ... over the host. Formerly captain of the guard, he had succeeded Josh as commander of the forces.
Zadok and Abiathar were the priests. The latter had been banished to his country seat, and retained nothing more than the name of high priest, Zadok having been promoted to the pontificate in his stead. In the course of the sacred history a double priesthood appears, the origin or cause of which arrangement is nowhere explained. Jewish writers say that the one was high priest and the other sagan, or deputy-as, according to them, Moses was of Aaron, and Annas of Caiaphas. In like manner, Zadok and Abiathar stood in the same relative position; but if there was a distinction between them, it must have been very slight, as these persons are always associated as equals in official dignity, as also were Eleazar and Ithamar, Hophni and Phinehas. The common opinion is, that Zadok had been appointed high priest by Saul, the latter by David; and that as a matter of policy both were retained as joint-pontiffs when the son of Jesse became king of all Israel. But there is no Scriptural authority for this hypothesis. Zadok is always mentioned first, the precedency being assigned to him probably on account of his belonging to the older branch of the Aaronic house, and of the superior influence of his ancestral house; there being among the sons of Eleazar sixteen chief men, and only eight among the sons of Ithamar, for the twenty-four courses (1 Chronicles 24:4).
As to the division of pontifical duties between them, Zadok appears to have ministered in the tabernacle at Gibeon (1 Chronicles 16:1-7; 1 Chronicles 16:37-40). Abiathar took charge of the ark at Jerusalem principally, though not exclusively (see the notes at 2 Samuel 15:24-29; 1 Chronicles 15:11). Abiathar must have been an old man at the time of Solomon's accession; and it is probable that owing to age and bitter mortification under the sentence of degradation, he did not long survive that public disgrace. Zadok, too, must have been advanced in life, considering that he was a "a young man" when he is first mentioned as joining David's party at Ziklag (1 Chronicles 12:28), and that not a single act of his is recorded in the history of Solomon's reign. We may conclude, therefore, that though nominally the high priest, he devolved the active duties of the pontificate on his grandson Azariah (1 Kings 4:2). The appointment of the high priest seems at first to have lain with the Sanhedrim or elders; but in the times of the monarchy the crown exercised the patronage.