The Book of Lamentations was once part of the Book of Jeremiah, and was also written by Jeremiah in 586 B.C. The key truth of the book is mourning, as Jeremiah mourned over the fall of Jerusalem and the destruction of Solomon's temple, and the historic time was the fall of Jerusalem. The key verse of the book is found in 3:22 and 23, "His compassions fail not. They are new every morning: great is thy faithfulness."