On what basis is instrumental music in worship, praise and testimony to be refused?
Worship and testimony are examples of the two–fold nature of the service of God. Worship and praise are what are priestly and testimony is what is Levitical. In both cases it is God’s service and thus must be carried out as He directs.
Under the Law these two sides were clearly seen. Meticulous detail was given as to how God could be approached, as to what offerings should be made and when and how they were to be carried out. This was the priestly side of service. Similarly, when the Ark and all associated with it was carried by the Levites in testimony through the wilderness, nothing was left to man’s imagination. All was under God’s ordering. It was God who was to be served and it was God who gave command as to how that service was to be carried out.
There was an occasion in the wilderness when two men thought that they would carry out that service differently. It says in Lev. 10: 1 that the priests Nadab and Abihu “presented strange fire before Jehovah, which he had not commanded them.” Their ideas were foreign to God because He had not commanded them. The result was that “they died before Jehovah”, (v.2). God must be served not as man thinks best, but as He has commanded.
Now musical instruments were certainly used in God’s service in the O.T., but is God to be served now as He was then? Not all were priests or Levites then; priestly and Levitical service is now open to all God’s people. Sacrifices were then offered for sins; now “[there is] no longer a sacrifice for sin”, (Heb. 10: 18). In John 4 the Lord Jesus converses with a Samaritan woman on the subject of worship. Needless to say His words are of the utmost importance. In verse 23 the Lord says “But [the] hour is coming and now is, when the true worshippers shall worship the Father in spirit and truth; for also the Father seeks such as his worshippers.” These words indicate that the whole nature of worship is to change from what it was previously. The “hour is coming,”—historically then still future as the day of Pentecost had not dawned, but the Lord also said “and now is” for morally He was already rejected, (John 1: 11), and it was all over with the old order. The moral conditions necessitating this radical change were already there. Yet did not the real worshippers worship in spirit and truth under the old economy? That cannot be the meaning of the words otherwise the Lord would have said something like "for the true worshippers always worshipped....". No, it is not a question of the reality of those who worshipped in the past but a radical change of the conditions for worship in the future. Previously God was not worshipped as Father, but under other names such as the Most High God and Jehovah. In v24 the reason is given for this change: "God [is] a spirit, and they who worship him must worship [him] in spirit and truth." Note the force of these words. He does not say that they who worship God should or ought to worship Him in spirit and truth, but those who worship God must worship Him in spirit and truth, IT IS NOT LEFT TO MAN'S CHOICE; IT IS DICTATED BY GOD'S COMMAND.
Well then, where in the Acts or in the Epistles is there any command or any example given of the use of musical instruments in God's service? Nowhere! What about the harps of Revelation? Those of say, Rev. 5: 8, cannot be literal harps otherwise the four living creatures and the golden bowls must also be literal. They are symbolic as Rev. 1:1 states: "he signified it" or "made known by signs".
All must now be "in spirit and truth". "In truth" is in keeping with the revelation that has been made by the Son; "in spirit" as determining the nature of the response. In the great epistle of approach, Paul speaks of the "new and living way", (Heb. 10: 20). If it is a new and living way, how I ask, can musical instruments which the same author elsewhere, (1 Cor. 14: 7), says are "lifeless things", have any part? In Hebrews Paul is writing to those who knew the old economy and he continually compares and contrasts it with the new. In Heb. 13: 15 I read "By him therefore let us offer [the] sacrifice of praise continually to God, that is"—and how does he go on to explain that mode of offering? By the piping of the organ or the plucking of the harp? No! but " by [the] fruit of [the] lips confessing his name." Do musical instruments confess His name? No! But has not our singing to have a musical accompaniment? Yes! But not with guitar or keyboard. In 1 Cor. 14: 15 the singing is to be accompanied, not with the organ, but "with the spirit" and "with the understanding".
Finally, it may be of interest to note that even in Christendom musical instruments were not used until many centuries after the Apostles' departure. Some may call their subsequent introduction "progress"—in reality it is a step back to Judaism.