The New Testament uses a number of different pictures of church: church is Christ’s body (Rom 12:5); it is a temple built with living stones (I Pet 2:5), it is a family (Eph 2:19).
The metaphor of family is very helpful.
Family is neither a building nor an event. Healthy families will get together often, but it’s not the get-togethers that make them family. It’s the relationships. We are family, we don’t do family. Families share life together. Their interaction isn’t limited to Sunday lunch. They love each other, live life together, share one another’s burdens, care for one another, at times they will reprove one another and teach one another.
Sounds like the “one anothers” of the New Testament.
Similarly, church is relationships, but the difference between church and any other set of relationships is the presence of Jesus. As Robert Fitts says in Saturation Church Planting:
When two or three true, born-again believers come together in His name, Jesus is in the midst. Jesus in the midst is church! It is a different experience than Jesus within. We cannot experience Jesus in the midst when we are alone. We can only experience Jesus in the midst when we are in company with others–at least one or two others.
But is it church in the fullest sense of the word? Yes, it is a church in the fullest sense of the word. It is the basic church. You can have more than two or three and it is still a church, but it does not become “more church” because there are more than two or three. It only becomes bigger church.