Between him, i.e. the Lord, as is sufficiently implied in the end of this verse, and plainly expressed 2 Kings 11:17. Or, between himself; that the people might see that he brought them under no bond but what he would take upon himself. That they should be the Lord's people, i.e. that every one in his place and station would maintain the law and worship of God, and root out all false worship; which they did in the next verse.
Related Commentaries of 2 Chronicles 23:16
2 Chronicles 23:16
16 And Jehoiada made a covenant between him, and between all the people, and between the king, that they should be the LORD'S people.