Jeremiah was the Old Testament suffering servant of the Lord. He witnessed the destruction of his own people, his home town, and watched the bodies stack up like so much cord wood. He knew his people deserved their punishment, but their suffering pained him to the depths of his being (which you see in several places in Jeremiah).
Lamentations is devoted in its entirety to the grief of Jeremiah (and therefore God, whose grief Jeremiah represents). Each of its five chapters is, in Hebrew, an acrostic. Each chapter but the third has 22 verses, corresponding to the 22 letters of the Hebrew alphabet. Each verse begins with a succeeding letter. In chapter 3, because it has sixty six verses, the first three verses begin with the first Hebrew letter, the aleph, the next three the second letter (Hebrew “bet”) and so on.
The grief of the prophet is profound. Think about it like this: A piano player has only so many keys. Whatever he plays must be played with what he has. So a grieving poet has only 22 letters. He must write with what he has. But, as a troubled piano player might stumble through his performance, so the poet, twice, stumbles in his poem (you see it plainly in the Hebrew text), mixing the order of letters in the middle of chapter 2 and chapter 4. By chapter 5, his talent fails him. Though he sticks with 22 verses (for the 22 letters), he no longer follows the successive order of letters.
Jeremiah wrote: “Oh, that my head were a spring of water and my eyes a fountain of tears! I would weep day and night for the slain of my people” (Jeremiah 9:1). The phrase is repeated somewhat in Lamentations 1:16, and Lamentations is Jeremiah’s suffering cry, a human reflection of the pain of God over His children who have decided to abandon the way of a blessing Father for the highway of fools.