פרק ד

There are 2 sections of this פרק.

In the first, א–י, we see how the precious children of ציון used to be golden, but now what has become of them? The people are at fault - they've gone from glorious to cruel, from wealthy to hunting in the garbage. ירושלים's no longer blaming G-d. She says that the sins of her people are even greater than the sins of סדום - she's acknowledging that ירושלים deserved to be destroyed like סדום, but it wasn't.

In the second section, יא–כב, the מקונן is pointing out the flawed leaders and the sins of the people as well. The leaders failed them - now they're blind and טמא. G-d punished them because they sinned - not for no reason. We turned to nations who betrayed us. Our punishment is almost over - but the enemies are going to be punished.

As we learned, this פרק matches up with פרק ב. The first section of this פרק matches up with the second section of פרק ב. The conditions are the same in both - people are starving, there are bad conditions, and the women are being immoral. But in the first half of ד, we see that there's a recognition that the conditions are because of the people's sins; whereas in the second half of ב, they were blaming G-d.
Additionally, the second section of this פרק matches up with the first section of ד. In both they talk about the anger, but in פרק ד they acknowledge that there's a reason for this anger, as opposed to ב where they thought there was no reason for it.

פרק ד adds a lot that wasn't included in ב - they're finally realizing that it's because the people sinned. It's going back over everything that happened before, just with a new perspective. This continues along the progression that we've seen unfolding: shock, anger, blame,  examine/evaluate, acceptance, move on. Right now we're in the evaluate and acceptance part.

It's interesting because we've seen the whole ספר so far that ירושלים is really unwilling to admit that anything is her fault, and is very stuck on the fact that G-d is angry and evil (and even seems little bit crazy). But now she's finally changing her mind.