Romans 15:9

and that the Gentiles might glorify God for his mercy; as it is written, Therefore will. give praise unto thee among the Gentiles, And sing unto thy name.

'and that' -'This is also why Christ came...He also came to give Gentiles reason to rejoice over God's mercy. There's no point in denying that because Paul is able to quote scripture to support the notion.' (McGuiggan p. 419)

'Let us be reminded of the fellow who wrote this. Paul had not been easily persuaded of this truth. He was Hebrew of the Hebrews and. Pharisee of the Pharisees! But once he accepted Jesus as his Lord, his attitude was: "Speak, Lord, thy servant heareth". And when he was commissioned as. special vessel to bear the name of Christ before Gentiles, kings, and the children of Israel (Acts 9:15), he did not argue or quibble. He went.' (Green p. 13)

'as it is written' -'Isn't it interesting to note that Paul viewed the Scriptures as the end of all argument? And isn't it also interesting that he thought it would hold sway with those around him. Whatever else the modern views of the Bible's authority are, they aren't first century. Men in those days (and before) thought the Scripture couldn't be broken. If the Bible said it, that was the end of that. And as I've already mentioned, such use of scriptures implies that the Scriptures have been transmitted faithfully throughout the centuries.' (McGuiggan p. 419)

'Therefore will. give praise unto thee among the Gentiles, And sing unto thy name'. Psalms 18:49 'It pictures the Christ Himself in the midst of the Gentiles, praising God.' (Green p. 13)

Point to Note:

It is interesting to note, that of all the 'music' passages that exist in the O.T., only the ones that mention 'singing' are quoted in the N.T. (See also Hebrews 2:12)