2 Samuel 8:17 - Joseph Benson’s Commentary on the Old and New Testaments

Zadok and Ahimelech were the priests That is, as some think, Zadok was the high-priest, and Ahimelech his sagan or vicar; or, according to others, neither of these was the high-priest, but they were both only the vicars of Abiathar, and heads of the sacerdotal families, the second priests, to use the language of Scripture, 2 Kings 25:18. The former was of the family of Eleazar, (1 Chronicles 6:8,) the other of Ithamar. The family of Eli was now declining fast; and in the next reign the other family was advanced to the high-priesthood, Abiathar and his posterity being quite thrown out. Seraiah was the scribe Or secretary of state, as we now speak. But Bishop Patrick observes, that as the word ספר sopher, which we translate scribe, imports something of learning, as the word scribe, so often occurring in the New Testament, also does, he takes Seraiah to have been the king's prime counsellor in the law. And others think there were two of this character, one an ecclesiastical and the other a civil scribe. Thus “the sacred writer no sooner gives us an account of David's executing justice and judgment, but he immediately adds a list of the great officers then employed by him. For a principal part of a king's wisdom, as well as of his felicity, consists in the choice of able ministers to discharge the great offices of the state.” Delaney.