Thanks for the good questions. I pray you find my answers helpful. If not, please let me know, and I will clarify as soon as I can.
you said that to introduce instruments a commandment from God was required as we see in II Chronicles 29:20-30, but where does it says that the lord authorized the use of instruments on II chronicles 16:1-42 ?
Let me answer with a question, beginning by looking at II Chronicles 29
And he stationed the Levites in the house of the LORD with cymbals, with stringed instruments, and with harps, according to the commandment of David, of Gad the king's seer, and of Nathan the prophet; for thus was the commandment of the LORD by his prophets. The Levites stood with the instruments of David, and the priests with the trumpets. Then Hezekiah commanded them to offer the burnt offering on the altar. And when the burnt offering began, the song of the LORD also began, with the trumpets and with the instruments of David king of Israel. (II Chronicles 29:25-27).
Where in the Bible can we read of David receiving this command from the Lord by way of Gad and Nathan? Where do we read of David having knowledge of God's will on such matters?
I can't find a verse that records the specific revelation from God; however, I think I Chronicles 15-16
indicate that David had clear direction and approval from God on his usage and arrangement of musical instruments by this point:
And David called for Zadok and Abiathar the priests, and for the Levites: for Uriel, Asaiah, Joel, Shemaiah, Eliel, and Amminadab. [TB: Why did he not call for Gad and Nathan? Maybe because they had already directed him?] He said to them, "You are the heads of the fathers' houses of the Levites; sanctify yourselves, you and your brethren, that you may bring up the ark of the LORD God of Israel to the place I have prepared for it. For because you did not do it the first time, the LORD our God broke out against us, because we did not consult Him about the proper order." [TB: Do you think David has consulted the Lord at this point? Clearly, he had not consulted the Levites. Whom had he consulted? Who else would it be beside "Gad, the king's seer" and "Nathan, the prophet"?] So the priests and the Levites sanctified themselves to bring up the ark of the LORD God of Israel. And the children of the Levites bore the ark of God on their shoulders, by its poles, as Moses had commanded according to the word of the LORD. 16 Then David spoke to the leaders of the Levites to appoint their brethren to be the singers accompanied by instruments of music, stringed instruments, harps, and cymbals, by raising the voice with resounding joy. ... So David, the elders of Israel, and the captains over thousands went to bring up the ark of the covenant of the LORD from the house of Obed-Edom with joy. And so it was, when God helped the Levites who bore the ark of the covenant of the LORD, that they offered seven bulls and seven rams. ... So they brought the ark of God, and set it in the midst of the tabernacle that David had erected for it. Then they offered burnt offerings and peace offerings before God. And when David had finished offering the burnt offerings and the peace offerings, he blessed the people in the name of the LORD. ... And he appointed some of the Levites to minister before the ark of the LORD, to commemorate, to thank, and to praise the LORD God of Israel: Asaph the chief, and next to him Zechariah, then Jeiel, Shemiramoth, Jehiel, Mattithiah, Eliab, Benaiah, and Obed-Edom: Jeiel with stringed instruments and harps, but Asaph made music with cymbals; Benaiah and Jahaziel the priests regularly blew the trumpets before the ark of the covenant of God. On that day David first delivered this psalm into the hand of Asaph and his brethren, to thank the LORD ... (I Chronicles 15:11-16, 25-26; 16:1-7)
My conclusion is that between the events of I Chronicles 13 and 15, David had finally consulted with God. Look at the above text? Do you see where David is "commanding" and "appointing" the usage of musical instruments? Do you see God's approval on the matter? Nobody is being struck dead. Furthermore, we see God's blessing. We learn that He "helped the Levites", and we see that David was inspired with a Psalm, delivered to Asaph.
In short, we do not read of God authorizing the instruments as appointed and arranged in I Chronicles 15-16. However, in II Chronicles 29, we read that David's arrangement was provided by a direct command from the Lord. Reading of David's confident arrangement, references to the Lord's direction, and the Lord's blessing in I Chronicles 15-16, I conclude that David received this command, as recorded in II Chronicles 29, between the events of I Chronicles 13 and 15.
If it did not occur then, when do you think it would have occurred?
I still don't understand how instruments were part of the law, can you explain that a little more to me? sorry...=D
To answer your last question, musical instruments were commanded under the Old Law (II Chronicles 29:25-27). They were associated with temple worship and sacrifice, especially surrounding the ark of the Lord (I Chronicles 15:16-24; 16:4-6, 37-42; Psalm 137:2-4; Ezra 3:10; Nehemiah 10:28, 39; 11:22; 12:27, 45). To bring back instrumental music would be paramount to restoring sacrifice, dances, incense, and linen ephods (Psalm 149:3; 150:3-5; I Chronicles 15:27-28). Where is the command to use instruments in the New Testament? I can read of God commanding vocal music - the instruments of the heart and voice (Ephesians 5:18-20; Colossians 3:16; James 5:13), but where is the authority for mechanical instruments in the New Testament?
For more on this point, please see our article on the difference between the Old and New Covenants:
http://www.insearchoftruth.org/articles ... ents2.html
I pray you find this helpful. If this does not answer your question, please let me know. I will be glad to elaborate. And, if I have overlooked something, you would be my friend for bringing it to my attention. I look forward to hearing from you soon.
May God help us to have a sincere love of truth,
BTW, here are a few forum posts on the topic of instrumental music, along with links to all of our articles on the subject: