Kitto's Popular Cyclopedia of Biblial Literature
Abi´athar (Father of abundance), the tenth high-priest of the Jews, and fourth in descent from Eli. When his father, the high-priest Abimelech, was slain with the priests at Nob, for suspected partiality to the fugitive David, Abiathar escaped the massacre; and bearing with him the most essential part of the priestly raiment, the ephod [PRIEST], repaired to the son of Jesse, who was then in the cave of Adullam (1 Samuel 22:20-23; 1 Samuel 23:6). He was well received by David, and became the priest of the party during its wanderings. As such he sought and received for David responses from God. When David became king of Judah, he made Abiathar high-priest. Meanwhile Zadok had been appointed high-priest by Saul, and continued to act in this capacity while Abiathar was high-priest in Judah. The appointment of Zadok was not only unexceptionable in itself, but was in accordance with the divine sentence of deposition which had been passed upon the house of Eli (1 Samuel 2:30-36). When, therefore, David acquired the kingdom of Israel, he had no just ground on which Zadok could be removed, and Abiathar set in his place; and the attempt to do so would probably have been offensive to his new subjects. The king got over this difficulty by allowing both appointments to stand; and until the end of David's reign Zadok and Abiathar were joint high-priests. As high-priest Abiathar must have been perfectly aware of the divine intention that Solomon should be the successor of David: he was therefore the least excusable, in some respects, of all those who were parties in the attempt to raise Adonijah to the throne. So his conduct seems to have been viewed by Solomon, who, in deposing him from the high-priesthood, plainly told him that only his sacerdotal character, and his former services to David, preserved him from death. This deposition of Abiathar completed the doom long before denounced upon the house of Eli, who was of the line of Ithamar, the younger son of Aaron. Zadok, who remained the high-priest, was of the elder line of Eleazer (1 Kings 1:7; 1 Kings 1:19; 1 Kings 2:26-27).
Kitto, John, ed. Entry for 'Abiathar'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/a/abiathar.html.