SERIOUS BUSINESS
There are certain things which are holy unto the Lord. These things are under his perview and are not to be profaned. What God has reserved for himself is not to be treated common by men.
Among these are his name; the sabbath; the ark of the covenant; the tabernacle/temple; his people; his worship. Those who violated the proper use of these were executed. God consider(-s, -ed) these capital offenses. They were just as serious as murder, idolatry, adultery, or sodomy.
God has always taken his worship seriously. Consider Cain and Abel or Nadab and Abihu. Consider what happened to Uzza or to Ananias and Sapphira. We must have authority for what we do in service to and worship of God.
Since we are under a New Covenant we must appeal to it for our authority. Instrumental music is wholly without authority as an element of worship in the New Testament church. To introduce such is to cause division for it cannot be done by faith.
Division is contrary to Jesus’ prayer for unity (John 17) and Paul’s admonitions (1 Cor. 1, 3). It is considered a defilement of God’s temple, the church. Those who defile the temple will be destroyed by God (1 Cor. 3:16-17).
This makes adding instrumental music to Christian worship extremely serious business.

