Date of Writing: A careful examination of the authorship question, as well as the subject matter covered by the psalms themselves, reveals that they span a period of many centuries. The oldest psalm in the collection is probably the prayer of Moses (90), a reflection on the frailty of man as compared to the eternity of God. The latest psalm is probably (137), a song of lament clearly written during the days when the Hebrews were being held captive by the Babylonians, from about 586 to 538 B.C. It is clear that the 150 individual psalms were written by many different people across a period of a thousand years in Israel's history. They must have been compiled and put together in their present form by some unknown editor shortly after the captivity ended about 537 B.C. Purpose of Writing: The Book of Psalms is the longest book in the Bible, with 150 individual psalms. It is also one of the most diverse, since the psalms deal with such subjects as God and His creation, war, worship, wisdom, sin and evil, judgment, justice, and the coming of the Messiah.