Amariah. According to 1 Chron. 6:8-11, Amariah was the fifth after Zadok, the high priest of David’s time (2 Sam. 17:15). Since Jehoshaphat was the fifth from David, the same Amariah is indicated in both instances.
Matters of the Lord. The high priest was the natural head of the high court in the matter of religious cases.
The king’s matters. Zebadiah was to be the head of the high court in all civil or criminal cases.
With the good. Jehoshaphat was expressing his faith that God would be with those who would be true to Him and upright in their service. The word for “shall be” should be translated as a wish, thus making the last sentence a benediction or prayer: “And may the Lord be with the good.”