24:1ff The Temple service was highly structured, but this did not hinder the Spirit of God. Rather, it provided an orderly context for worship. (Compare 1 Corinthians 14:40.) Sometimes we feel that planning and structure are unspiritual activities that may hinder spontaneity in worship. But order and structure can free us to respond to God. Order brings glory to God as we experience the joy, freedom, and calm that come when we have wisely planned in advance.
24:3 This Ahimelech was the son of Abiathar and the grandson of another Ahimelech, one of the priests massacred by Saul (1 Samuel 22:11-18). Abiathar and Zadok were co–high priests under David: One was at Jerusalem where the Ark of God was kept, and one was at Gibeon serving at the Tabernacle. It appears from this verse and 18:16 that Ahimelech began to assume some of Abiathar’s duties as his father grew old.
24:4 Eleazar’s descendants were divided into 16 groups (as opposed to Ithamar’s 8) for three reasons. (1) Eleazar had received the birthright since his two older brothers, Nadab and Abihu, had been killed (Leviticus 10). The birthright included a double portion of the father’s estate. (2) His descendants were greater in number than Ithamar’s. (3) His descendants had greater leadership ability. These 24 groups gave order to the functioning of the house of the Lord.
24:7-18 Each of these 24 groups of priests served two-week shifts each year at the house of the Lord. The rest of the time they served in their hometowns. This system was still in place in Jesus’ day (Luke 1:5-9). Zacharias was a member of the Abia (or Abijah) division. During his shift at the Temple, an angel appeared to him and predicted that he would have a son, John.