More than once, someone has said "I don't have to find 'authority' in the Bible for a building a rec-room onto our church's building! It helps us spread the gospel by encouraging kids to come meet here. You hypocrite; you can't even find authority for a building in scripture, but you meet in one!" The reply should be immediate: "If we don't have authority for a building, we ought not to have one! …But we do."
Ancient Israel was told, "Whatever I command you, you shall be careful to do; you shall not add to nor take away from it," Deut 12:32, and that principle is found throughout scripture. We are to carry out God's commands, and not deviate from them—that is the key to the distinction between an "aid" (often called an "expedient") and an addition: an aid legitimately helps to carry out His command, but does not change it; an addition fundamentally changes the command.
For instance: we are to sing as a local church, "speaking to one another in psalms and hymns and spiritual songs, singing and making melody with your heart to the Lord," Eph 5:19 (cf Col 3:16). To carry out that command, we may use song books, a song leader, a pitch pipe, and sing with harmony or as a chant—none of these change the command. They are aids. But to accompany with a piano or guitar is an addition; you are no longer singing, but playing as well. Interestingly, the two actions are independent: you can take away the singing, and still be playing an instrument to worship God… but not with His authority under the New Covenant.
We have authority for a common collection taken up on Sundays freely given by the local church's members: "On the first day of every week each one of you is to put aside and save, as he may prosper, so that no collections be made when I come," 1 Cor 16:1-4. We might have baskets or trays in which to take up the collection; or we might have a box with a hole drilled in it available for brethren to drop their money in—those are just aids to the command. But to have a bake sale, goat stew supper, some form of tax, or any other means of collecting funds would be an addition, and without authority.
So, what might identify something as a legitimate aid? Obviously, it can't be sinful in and of itself; Christians are told: "…do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God," Rom 6:13.
An aid also can't be specified. God told Noah to build an ark of gopher wood—what he was told to build was specific: it was to be an ark, not a clipper ship. And it had to be of gopher wood; no other kind of wood would do. On the other hand, how it was to be built was generic: Noah could use whatever he wanted—hammers, chisels or saws, with his sons for labor, or hired hands.
And a genuine aid has to edify: "…Let all things be done for edification," 1 Cor 14:26b (cf 1 Cor 10:23-33). That, of course, means that it must not cause brethren to stumble, or sin. Paul wrote, "Therefore, if food causes my brother to stumble, I will never eat meat again, so that I will not cause my brother to stumble," 1 Cor 8:13. If Paul would forgo eating meat to keep a brother from stumbling, there should be no question that if an "aid" would cause division or sin, it is not an aid—it is destructive.
What about the use of a church's building? Again, if we don't have authority for one, we ought not to have one! …But we do. We are to meet as a local church: "…let us consider how to stimulate one another to love and good deeds, not forsaking our own assembling together, as is the habit of some, but encouraging one another; and all the more as you see the day drawing near," Heb 10:24,25. The text doesn't mention in what venue; simply not to neglect meeting with one another. So, it is irrelevant if we rent a storefront, borrow a library room, meet in a home, or buy a building as a local church—they are aids to the command, and we have authority for any one of them inherent in the command to meet.
What we do not have, however, is authority for a gym, kitchen, "all-purpose" or rec-room, because there is no authority in scripture for the local church to plan and provide for social activities. These aren't things that should draw us to God; it is the gospel itself—Scripture—that is "the power of God for salvation to everyone who believes," Rom 1:16.
Jesus said that at the end of time, many will have done some impressive things, claiming they were done in His name—i.e., they thought they were acting by His authority, lawfully, within His will (cp Acts 19:13; 2:38). Sadly, they were not; ultimately, he will tell them: "I never knew you; depart from me, you who practice lawlessness," Mt 7:23. Whatever we do or say should be in His name, Col 3:17; and nowhere should that principle be more easily understood than in how we work and worship together as a local church.
