We are NOT called to preach a message, we are called to live that message... Study the prophet Jeremiah. He resisted the calling. He was insecure and gave God a million reasons why he couldn't do it. But, God never wavered. We are often consumed with who we are and what we are not. We know all of our failures and faults, but God doesn't seem to be moved by that at all... 

Some of the greatest leaders in human history were imperfect people. 

But to fully live in this life, the only thing that satisfies us is living larger than what WE can do, or what we KNOW.