Lamentations is unique as a Book of the Bible. All five chapters are poetry, but unlike Psalms, they all have the same theme. Each chapter is an acrostic poem. There are Psalms that follow this pattern. Each chapter uses the letters of the Hebrew alphabet as a structural platform. In Chapters 1, 2, 4 and 5 each has 22 verses with each verse beginning with the next successive letter of the alphabet, Aleph, Beth, Gimel, etc. Chapter 3 has 66 verses and the verses are grouped by threes. He continues the use of the letters to in succession to shape the poem. (This pattern only works in Hebrew.)
He refers to the former glory of Israel, her armies, her Kings, but he mourns what has happened to her people. He repeatedly calls to mind the sins which led to this disaster and reminds the people they knew there would be consequences, but they flaunted God's laws.
In Chapter 3 he returns to a joyous exclamation of hope. The Lord's mercies have kept us from complete destruction. My soul claims hope in him. It is good to hope and wait patiently for the salvation of the Lord. Even though he has allowed grief, he will also show compassion. He does not enjoy afflicting us, but this is the result when we rob men of justice. (The Living Bible, Lamentations:21-26.)
Read Lamentations and repent. Seek God's forgiveness. Live in obedience. Revel in the joy of grace.