In this chapter, several dynasties rise and fall in the northern kingdom, Israel.
This chapter continues with the political intrigue that we saw in the northern kingdom in the previous chapter. Jehu prophesies that Baasha's entire family would be destroyed because he "walked in the way of Jeroboam" and "because he struck it" (v. 7), referring to Baasha destroying the house of Jeroboam. This feels a little ironic, that God would at one time declare that Jeroboam's whole family would be destroyed, which Baasha does, and then say that Baasha would be destroyed for what he did to Jeroboam. To make a long story short, Baasha acted treacherously towards Jeroboam's family and even though God had prophesied that Jeroboam and his whole family would die, he did not command Baasha to do it, so Baasha was still acting sinfully in this regard. Even in the things that God has commanded to happen, we sin if we try to take those things on our own initiative rather than act in accordance with God's will for us. It's like when God prophesied a famine in Pharaoh's dream, imagine if Joseph had gone out and tried to poison the granaries to fulfill what God declared would happen. In that case, Joseph would have been sinning even if he was fulfilling a judgment of God because in the vast majority of cases, it is not a human responsibility to bring about God's judgment on the earth.
Baasha himself survives and dies in his old age, but his son is acting irresponsibly, "drinking himself drunk" in an official's house, when he is assassinated by one of his commanders. Like what Baasha did to Jeroboam, Zimri kills Elah's entire family, the entire household of Baasha, and in that sense Zimri brings upon himself the same condemnation that followed Baasha's family.
Remember back in the book of Samuel when David permitted Mephibosheth to live in Jerusalem and eat from his table? Remember how I said this was an extraordinary kindness? This chapter shows us how coup plotters typically deal with the families of their victims. So on the one hand, David acted with great kindness. On the other hand, I also mentioned how risky it was for David to leave a descendant of Saul alive, because any relative of Saul could possibly rally those men (especially the tribe of Benjamin) that maintained loyalty to the house of Saul and could be a threat to David's own life and family.
It is doubtless that Baasha and Zimri are thinking about this when they destroyed the families of the previous king: the easiest way to ensure that there is no retribution against oneself is to kill all possible survivors of their treachery. It's ironic, then, that by killing Jeroboam's family, Baasha had ensured that God would be the one to take retribution against him. Similarly, one could imagine that if David had killed all the household of Saul, he would have brought God's wrath against himself. By showing mercy (contrary to human wisdom and cultural standards of the time), David had guaranteed God's protection of his dynasty.
Unlike the previous coup, Zimri is not able to rally support; instead, the army follows their commander Omri, who kills Zimri. After that, Omri gets into conflict with Tibni, who also dies and Omri becomes king. We should understand that this was a very violent period of time in Israel's history.
Nevertheless, the strife finally ends when Omri becomes king. Even though Omri leads Israel into sin, he reigns for 12 years and his son reigns after him. Note how all of these various kings were reigning in the time of Asa? This means that during this whole window of 30-something years, Judah has a single king, Asa, while the northern kingdom goes through Nadab (the son of Jeroboam), Baasha, Elah, Zimri, Omri, and lastly Ahab. This is a striking contrast between the political stability of the south and the instability of the north, as well as the violence that comes with that instability. As if the Aramean invasion is not enough, the men of Israel are spending an awful lot of time killing each other too.
The chapter concludes with a throwback to a prophecy by Joshua in Joshua 6:26. It doesn't tell us how or when it happens, but the person who rebuilt Jericho loses two of his sons in the process. I can't say much because we don't really know any of the details, but I should mention that Jericho is in the northern kingdom, Israel, and it is definitely possible that his sons were killed in the political violence that I just mentioned.
This is the context in which Ahab becomes king, introduced alongside his wife Jezebel (a Sidonian, who is not an Israelite), and they are worshipers of Baal and Asherah. This sets us up for one of the longest stories in the book of Kings, the story of Ahab, Jezebel and Elijah. It is a story that will be filled with conflict between the idolatrous tendencies of the king and Elijah calling the people to follow the LORD.