“The Church exists for nothing else but to draw men into Christ, to make them little Christs. If they are not doing that, all the cathedrals, clergy, missions, sermons, even the Bible itself, are simply a waste of time. God became man for no other purpose.” C.S. Lewis
I would actually say that the church exists for four purposes. But the purpose Lewis mentions above (mission) is certainly one of the four... and sadly, it's the one that's most often neglected.
We need to pray and serve and love and work towards a greater impact in this sin-sick, death-weary world. Too often we talk about mission, and then fool ourselves into thinking that because we've talked about, we've done it.