Talk about cleaning house. While in the past we see the king take the initiative in ensuring that God's will would be done and that order was established in the land, here it is the high priest who takes the reins and reinstates the king, drives out the false queen, Athaliah, and throws out the gods and their temples and reinstates not only the political king but also the presence of the Lord as the sole presence of the deity. Jehoiada is the reformer who brings back that which the Lord wanted from Israel all along.
The most pernicious cycle that we see happening in the life of Israel is that they do that which is evil in the sight of the Lord which primarily consists of worshipping false gods. God raises up someone to bring order and a refocus on the priorities of the people of God, that person reigns and then they die and then confusions reigns.
We find ourselves in the state where Athaliah is dethroned. She enters the temple and see that Joash is being crowned the new king, he was the son of the king after all, and she yells treason expecting the crowd in the temple to follow after her. Well, they do follow after her but only to kill her. Joash is now king and we hope that this also means an instilling of peace and the pursuit of God as a result. Let's see what happens next.