Why did the early church gather? What did they do? What clues are there in Scripture?
Eric at A Pilgrim's Progress is exploring this question as well:
A Pilgrim's Progress: The Church's Primary Activity
I've understood that the Roman Catholic Church had the Eucharist as the main purpose of their gathering. And there is scripture to support the idea that the early church also celebrated the Lord's supper regularly when they gathered (however it likely looked more like a shared meal than what we typically see today).
Today, most churches I've been a part of have seem to view the sermon as central to the gathering. There may be some singing, prayer, and scripture reading before and after it, but the sermon is often viewed as the main course. If you come late for the singing but don't miss the sermon you didn't miss 'church'. Or if you miss 'church' you can listen to the sermon online or on CD.
I found Eric's observations of a few verses helpful (I Corinthians 14:26, Hebrews 10:24-25, I Timothy 4:13, Ephesians 5:18-21, I Corinthians 12:4-11) :
The above passages tell us something that might surprise us - especially in light of modern church gatherings: When the N.T. church gathered, they did not have a primary activity.So maybe there are a number of good things we can do when we gather, but we should let one good thing rob us from missing out on more. May we seek to build one another up to maturity in Christ using the different gifts God has given each of us. I believe we need one another, and that is why I want to gather with Christ's body.
It certainly wasn't preaching. It wasn't singing. It wasn't giving of testimonies. It wasn't reading scripture. It wasn't the Lord's Supper. It wasn't any one thing.