Not as a great warrior or mighty king did David win the everlasting love of our people, and indeed of all peoples on earth, but as the author of the Book of Psalms (Tehillim), the sweetest poetry of Israel.
King David was a link in the continued transmission of the Torah, being the spiritual successor to the prophet Samuel. He surrounded himself with a group of prophets and scholars and together they studied the Torah. He thought nothing of the comforts of life that his regal palace could offer him, and unlike other kings he would rise before the sun to pray and chant psalms of praise to G‑d, the King of all kings.
The Psalms are hymns of praise to the Almighty G‑d, Creator of the Universe. They speak of G‑d's greatness, His goodness and mercy; His power and justice. David pours out his heart in these Psalms and avows his sincerest and purest trust in G‑d alone. Many of the Psalms are prayers and supplications to G‑d which king David prayed in times of trouble. Some psalms contain good advice, showing the way of true happiness through virtue and the fulfillment of G‑d's commandments.
Thus the Psalms reflect all the varied incidents that can happen in life, both to the individual and to the whole Jewish nation. Indeed, in the history of David
-- his exile, persecution, struggles, and eventual triumph -- the Jewish people, collectively and individually, find an example and prophecy of their own life. No wonder the Book of Psalms has throughout the ages served as a boundless source of inspiration, courage, and hope.
Not all the Psalms were composed by king David. Some were composed by Adam, Shem, Abraham, Moses
and others. King David collected them all and added the psalms of his own which he had composed by Divine inspiration.
The Book of Psalms is divided into five parts, parallel to the Five Books of Moses. It is further subdivided into seven parts, one for each day in the week, and further divided into 30 divisions, for each day of the month. Many Jews make it a habit to say a portion of the Psalms every day after the morning prayers, thus completing all the Psalms in the course of a week or a month.