In this chapter Moroni takes Pahoran to task for not sending help to the armies. He condemns Pahoran for "sit[ting] upon [his] throne in a state of thoughtless stupor" while thousands of Nephites are dying in Pahoran's defense. Now, it's really easy to think that Moroni is being too harsh because we know that in the next chapter Pahoran explains what is going on and Moroni forgives him. But I am trying to see things from Moroni's point of view and I can see why he is so upset.
It's also interesting to compare this latter from Moroni to the one he wrote to Ammoron. In both, he is experiencing righteous anger. But in the one Ammoron, he was speaking to a wicked mad, and in this chapter, he is speaking to Pahoran, who he believes to be righteous, or at least knows that he used to be righteous. So a lot of this chapter comes across as calling Pahoran to repentance and telling him to shape up, just in very harsh terms.
I like what Moroni says in vs. 23: Now I would that ye should remember that God has said that the inward vessel shall be cleansed first, and then shall the outer vessel be cleansed also. I've always liked the metaphor of the clean cup. We can look good on the outside and still be filthy on the inside, and vice versa. But we should strive to be as clean as possible on the outside and the inside.
Moroni closes with a powerful statement that shows that he knows who he really answers to in the end: God, not the government leaders. I seek not for power, but to pull it down. I seek not for honor of the world, but for the glory of my God, and the freedom and welfare of my country. I really admire Captain Moroni for his zeal and continual righteousness and I hope to emulate him in my own life.