In this chapter, Jerusalem is burnt to the ground and nearly all the people are killed or exiled.
To speak honestly, this chapter simply reeks of hopelessness and despair. Jerusalem: destroyed. The king: blinded and imprisoned, with his sons put to death. The people: cast out from the land of promise. This is all of their worst fears come to life, all of the things threatened in Deuteronomy if the people rebelled, all of the things threatened by the prophets, all of the consequences of sin and idolatry. There was a time when Moses said, "I have set before you life and death, the blessing and the curse. Therefore choose life, that you and your descendants may live." (Deut 30:19) What we can see here with stark clarity is that Judah (as well as the northern kingdom Israel/Samaria) chose death. They chose to rebel against God (like Adam) and like Adam, they are now confronted with God's curse as a result of their actions.
If my readers remember, God originally established the covenant with Israel in order to draw them back into a proper relationship with him. Man was supposed to live in community with God; that community was broken when Adam sinned. God sought to restore it by establishing a covenant first with the patriarchs (Abraham, Isaac and Jacob) and then later with the entire nation of Israel (the story in Ex 19-24). I think it is important for my readers to understand that the fundamental deal God offered to Israel is very similar to the situation that Adam was placed in. God basically told Adam, "hey Adam, I am going to bless you, here is a great wife, you can possess the whole earth and multiply and do all these fun things, just don't sin by eating from a particular tree or else you will die." Adam goes and does exactly the thing God told him not to, and so he dies and the world is thrown into chaos. God says to himself, "that did not go the way I wanted it to." And so God sets off and he finds Israel, and he says to Israel, "hey, so things didn't work out between me and Adam. But you look pretty cool, how about you guys come back to your own personal garden of Eden in the promised land, I will bless you with anything you could ever hope or dream to have, and you guys follow me. The only law is that you should not sin and put me before all other gods, or else you will die." What we've learned over the last few books (well, basically everything between here and Exodus 32, inclusive) is that Israel delves right back into sin, following Adam's footsteps into darkness and similarly following Adam into the promised death.
Now, there are some differences; the sin is different, the way death happens to them is different, and a lot of the superficial circumstances are different. But I think these two stories are fundamentally very similar. In both cases God was bringing people into relationship with himself, in both cases there was a choice between life and death, in both cases the people involved chose death, and in both cases they were cast out of their homeland (Eden in one case, the promised land in the other) to a dark and uncertain future.
I could imagine someone asking, "if God saw how things worked out with Adam, why would he try again with Israel?" There are numerous answers to this question, but for the sake of time I will only offer one: God is trying to establish through the Old Testament (OT) the human need for a savior. Basically, the way I read it is this: if we had only seen Adam sin, then perhaps people would say, "well Adam sinned, but I will not repeat his mistake! God is condemning all of mankind for the actions of a single individual, and he is unjust to do so. I will act righteously." When we look at Israel, God blessed them in many ways, he provided for them, he delivered them from slavery in Egypt (which is symbolic of death, similar to how Adam was cast out of the garden) and he brought them into the promised land, to the "new Eden" for them to inhabit, cultivate, to be fruitful and multiply. And even after all the blessing, Israel sins again and again, harming one another and forsaking God in exchange for worthless idols. Moses interceded for the people many times, forestalling God's wrath, but never averting it entirely and now that wrath has come.
What Israel shows us is that sin is not some kind of accident like Adam was walking along and he suddenly tripped and his mouth landed on the forbidden fruit, and it all happened so fast and he couldn't help it, and he's really very sorry and he promises it would never happen again! To Adam, sin was a deliberate choice, perhaps a regretted choice but one he made nonetheless, and in the thousands of years since it was a choice repeated by every generation. That is the message of the OT. God could keep forgiving, keep restraining himself, and mankind would just keep sinning. There is no amount of second or third of fourth chances that would ever be enough for us to "figure it out" and stop sinning, and sin is not the result of harsh or burdensome circumstances. We do not sin because of our bad childhood or poverty or any circumstantial factor. God blessed Adam and he blessed Israel to show us that sin is not the result of hostile conditions, it's due to the innate tendencies of our own hearts. As the book of Judges puts it, everyone "doing what was right in his own eyes", choosing his own path and making his own decisions about what is good or bad instead of following God's standards for good and bad.
The OT establishes the need for a savior, someone who can come unadulterated by our sinful tendencies and help bring us back into proper relationship with God. Someone like the high priest who goes into the temple and makes atonement for the people, like on the day of atonement (Hebrew, "Yom Kippur". Lev 23:26-32)
Kings is not the end of the OT (in fact, we're barely halfway done), but in many ways I think the Babylonian exile is the thematic heart because of all these patterns that I just discussed.
The destruction of Jerusalem itself follows many of the same patterns as in the previous chapter, except more extreme. This time, rather than simply pillage Jerusalem, they steal everything and burn the city to the ground. The temple, palace and every good house is destroyed with fire. The people are again exiled, but instead of 7,000 leading men, the king of Babylon takes away the majority of the people. Now only a handful are left in the land. The chief officials (who led the rebellion) are put to death rather than exiled, and Judah is not given a new king. Gedaliah is appointed as a governor under king Nebuchadnezzar's authority. Judah no longer possesses even nominal independence, as punishment for their second revolt.
Some men go and assassinate Gedaliah and it's not entirely clear to me why. The bible doesn't really say, but there are two motivations that suggest themselves: first, it's possible that Ishmael killed Gedaliah because Gedaliah was collaborating with the Babylonians. Second, it's possible that Ishmael killed him in order to steal money and (as we will later discover in the book of Jeremiah) to take slaves. Because Ishmael is a brigand, essentially. Between these two, the first explanation makes a bit more sense to me personally (since Ishmael is a member of the royal household in v. 25 and probably loyal to Zedekiah), but it's hard to say for sure.
The last paragraph in the book ends on a slightly more hopeful note, telling us that 37 years into his exile, the king of Babylon (Evil-Merodach, a successor to Nebuchadnezzar) honors Jehoiachin with a favorable position and royal food. Jehoiachin is the king who was exiled before Zedekiah (in the previous chapter: 2 Kings 24:15); there is no evidence that Zedekiah was ever freed from prison, and he probably died in disgrace.
And with this, the book of Kings concludes. We are left in hopeful expectation for a salvation to come from God, both to free Israel from their captivity in Babylon as well as to free all men from the captivity of sin and death. The book of Kings (and the OT in general) leave us with a firm knowledge of the problem: sin. Now we must wait for God's answer; how will God bring about this great salvation?