Psalms is the second of the Wisdom books and the nineteenth book of the Old Testament. Written by King David, it 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.
It is a collection of prayers, poems, and hymns that focus the worshiper’s thoughts on God in praise and adoration. Parts of this book were used as a hymnal in the worship services of ancient Israel. The musical heritage of the psalms is demonstrated by its title. It comes from a Greek word which means “a song sung to the accompaniment of a musical instrument.”
(Note: Description used with permission from www.gotquestions.org)