If you want your church community life to be healthy, then keeping it free of vision, goals and purpose is a high priority.
This is how I spent most of my effort during my time in the professional ministry as a pastor. It took a great deal of discernment, courage and will from me and my team and others to make sure that our church community didn't sink into this terrible vortex of purpose-drivenness.
What I've discovered and conclude is that you can't expect to determine this at the beginning and forget about it, as if you've implemented an immutable unbreakable law that has set the character of your community in motion forever. It will be constantly challenged from the beginning. Like the victimization of grace upon which the law incessantly attempts to invade and encroach and replace... often successfully likewise your community will be ceaselessly tempted to allow just a little purpose, some kind of goal or a vision.
I promise you that one speck of this yeast will work its way through the whole batch of dough and change your community completely and forever. It will be practically impossible to go back. It will be as difficult to remove this infection as it would be to remove the yeast after the dough is risen.
*if you want to read more about my view of "vision", type "vision" in the search box.