Musical instruments should
not be incorporated into New Testament worship
because in the new covenant Christians are
in the spirit of the Levitical priesthood.
As Christ taught us, "But the hour cometh, and now is, when the true worshippers shall worship the Father in Spirit and Truth: for the Father requireth even such to worship him. God is a Spirit, and they that worship him, must worship him in Spirit and Truth." (
John 4:23-24) He is specifically addressing worship in the the context of this passage - that neither the corrupted worship of the Samaritans nor the Levitical Temple worship will be acceptable when Christ finishes His earthly ministry: "Jesus said unto her, Woman, believe me, the hour cometh, when ye shall neither in this mountain, nor at Jerusalem worship the Father." (v.21) I find the Geneva notes on v.23 helpful here: "...he speaketh of (Truth) not as we set it against a lie, but as we take it in respect of the outward ceremonies of the Law: which did only shadow that which Christ performed indeed."
Thus Paul instructs us: "Wherefore, be ye not unwise, but understand what the will of the Lord is. And be not drunk with wine, wherein is excess: but
be fulfilled with the Spirit, speaking unto yourselves in Spiritual psalms, and hymns, and songs, singing and
making melody to the Lord
in your hearts, giving thanks always for all things unto God even the Father, in the Name of our Lord Jesus Christ (
Ephesians 5.17-20).