Can a church consist of just one person?
A church is an entity separate and distinguishable from a single individual Christian. This can be seen in separation of responsibility seen in I Timothy 5:16, "If any believing man or woman has widows, let them relieve them, and do not let the church be burdened, that it may relieve those who are really widows." It can also be seen in the separation of funds. "Now concerning the collection for the saints, as I have given orders to the churches of Galatia, so you must do also: On the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come" (I Corinthians 16:1-2). A command was given to the churches that individual Christians were to give a portion of their prosperity on Sundays to be stored by the churches for later use in benevolence. Ananias and his wife sold some property and gave a portion of it to the church, but they lied about how much they gave. Peter told him, "While it remained, was it not your own? And after it was sold, was it not in your own control? Why have you conceived this thing in your heart? You have not lied to men but to God" While the property and then the money received from the property was in his possession, Ananias could have done as he would with it. However, things changed when it was given to the church. It was no longer his own; it belonged to God.
Another verse showing the distinction of an individual Christian, a group of Christians, and the church is see in the rules for handling problems between members. "Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. But if he will not hear, take with you one or two more, that 'by the mouth of two or three witnesses every word may be established.' And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector" (Matthew 18:15-17).
The word "church" is a collective noun, both in the Greek and in English. A collective noun is a singular word that represents a plurality, just as "herd" represents a group of livestock. In Greek the word is ekklesia, which literally means "the called out" or an assembly. It is not exclusively used for a religious body. When a mob stirred on the streets of Ephesus, it was called an ekklesia (Acts 19:32). Because of this word, we understand that a church cannot be an individual. One cow doesn't give a farmer a herd; one person having a tantrum doesn't create a rioting mob; and one Christian cannot assemble as a church.
Other terms indicate the multiplicity of Christians in a church. Local brethren are in fellowship (a sharing). They come together or assemble as a church (I Corinthians 11:18). They share in the partaking of the Lord's Supper. "The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? For we, though many, are one bread and one body; for we all partake of that one bread" (I Corinthians 10:16-17). The church benefits from having different people, with different talents, working together for a common purpose. "For in fact the body is not one member but many" (I Corinthians 12:14). This last verse is speaking of the church (the body) in a world-wide sense, but same point remains when we talk of local assemblies of the church.
Consider this, if a church was compose of just one person and that person sinned, how would the "church of one" withdraw from the sinner as commanded in I Corinthians 5:1-5)? How can an individual cease to fellowship himself? The answer is that he cannot. A single person cannot constitute a church.