Joining a Church

Why do you need to "join" a church? I mean is there a spiritual reason behind joining?  Or is it so the pastor can puff up their feathers and say that their church has x number of members?

Don't take this to mean, "Do I need to go to church?"  Because I do believe in "not forsaking the assembling of ourselves together" (Hebrews 10:24-25 KJV).  We should meet together and spur each other to good works as that same passage says.  Furthermore, Proverbs 27:17 (NIV) tells us that iron sharpens iron and one person sharpens another.  So we NEED that fellowship with other believers. But do we NEED to be a member of a church?

This is how I see it, we are called to be one body of believers.  And a lot of times different churches feel that they are better than others.  I believe that "membership" in a church can help spur this on.  Furthermore, you may primarily go to one place of worship, but what about when you are out of town on a Sunday?  What then?  Are we left to the wind?  Are we violating our "membership" by attending another congregation?  What about another church's bible studies?  Can we attend them or would that offend our "members"?  A church is not some exclusive club with members but rather a part of the body of Christ.