This post is a continuation of an ongoing series discussing "Bible Authority", you might want to consider reading Part 1, Part 2, and Part 3 before you proceed:
It must be understood that there are limits as to the range of authority in the realm of expediency. That range is defined as “Generic Authority” and “Specific Authority.” Generic Authority allows for choices within the general area indicated. Specific Authority authorizes only that which has been specified. The details of what has been commanded are the principles of these terms. An example of “generic authority” would be the use of a baptistery in order to fulfill the command to immerse one in water for the remission of his sins (Acts 2:38). The command is to be baptized in water (Acts 8:37). But, the Bible is not specific as to what body of water is to be used. It could be a baptistery, pool, lake, river, etc. in fulfilling the command. An example of “specific authority” would be the sacrifice of a lamb at the Passover (Exodus 12). To use any other animal when God specified a lamb would be counted rebellion against God’s authority.
First, the expedient must NOT be an addition to what the Word of God authorizes. There is a difference between an aid (expedient) and an addition. For example: The Bible commands, “…Go ye into all the world, and preach the gospel to every creature” (Mark 16:15). One could obey the command to “Go” by walking, riding, or even flying. All of these options have a direct relationship to the commandment to “Go” but no particular relationship to each other. Therefore each option would be authorized to carry out the obligation to “Go.” An illustration from the area of perception can help one to better understand this truth. One can perceive by hearing and one can perceive by seeing. Both are ways of perceiving. But, hearing is not an aid to seeing, nor is seeing an aid to hearing. These are both definite, distinctive ways of perceiving. Either one can be done without the other. Now, a hearing aid would be expedient to hearing just like eyeglasses would be expedient to seeing.
The realm of expediency is often referred to when trying to justify the use of mechanical instruments as an aid in the worship of the church. There is no doubt that God commands music in the church. Paul wrote, “Speaking to yourselves in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord;” (Ephesians 5:19). The music specified in this passage is singing. Singing is a definite, distinctive way to make music. Playing a mechanical instrument is also a definite, distinctive way to make music. Either one can be done without the other. Singing is not an aid to playing, nor is playing an aid to singing.