According to the author of 2 Kings, Jehoiada, a good priest, wanted to protect a young king from danger, so he called important people to the temple, made them promise to help, and showed them the hidden prince. This way, everyone knew who the true king was, and they could help keep him safe.
2 Kings 11:4: And the seventh year Jehoiada sent and fetched the rulers over hundreds, with the captains and the guard, and brought them to him into the house of the LORD, and made a covenant with them, and took an oath of them in the house of the LORD, and shewed them the king's son.
This verse highlights the concept of being either with Jesus or against Him, which contrasts with the alliance and cooperation seen in 2 Kings 11:4 when Jehoiada unites forces to protect Joash.
Matthew 12:30: He that is not with me is against me; and he that gathereth not with me scattereth abroad.