King David instituted a ministry of prophesy made up of two hundred and eighty-eight musicians directed by Asaph, Jeduthun and Heman (1 Chronicles 25:1-7). Asaph is known to have written Psalm 73, but surely he, Jeduthun, Heman and the nearly three hundred musicians of the ministry composed many more over the thirty-three years of David's monarchy and over the first quarter of Solomon's. Asaph, Jeduthun and Heman outlived David by more than a decade (2 Chronicles 5:12).
David had three major prophets at hand who heard the word of the Lord. They were Nathan (2 Samuel 7:1-17) Gad (2 Samuel 24:10-12) and Ahijah the prophet of Shiloh. Moreover he also had three "seers": Jeduthun (2 Chronicles 35:15) Heman (1 Chronicles 25:5) and Zadok the priest (2 Samuel 15:27).
David then had a highly qualified team to help him write the primitive book(s) of Moses during thirty-three years of peace in Jerusalem with a divine assurance of military success everywhere (1 Chronicles 18:1-13).
The protracted survival of David's liturgy underscores his preeminence. During the purification of the Temple three hundred and twenty years after David's death Hezekiah stationed his musicians as David, Gad and Nathan had prescribed and the Levites praised the Lord with the words of David and Asaph (2 Chronicles 29:20-30). Josiah celebrated a grand Passover a hundred and ten years later and he posted his musicians as David, Asaph, Heman and Jeduthun had prescribed (2 Chronicles 35:15). Jerusalem held a ceremonial thanksgiving for its rebuilt wall ca. 445 B.C. during which the priests, the Levites, the singers and the gatekeepers acted "according to the commands of David and his son Solomon" (Nehemiah 12:45-46; see also Ezra 3:10).
Three thousand years after David's monarchy religious Jews still heed the Law of Moses. Yet Judges 2:7-10 (recall the Introduction) say that the generation that grew up after Joshua's death no longer observed it!
The Law of Moses did not originate with Moses or with Joshua but with King David and his literate staff of "prophets" and "seers."