You can read his blog post about this challenging decision he has made. (http://eric-carpenter.blogspot.com/2010/09/reasoning-for-resigning.html ) I recommend that you take the time to read through the comment section as well, as Eric takes the time to answer some questions from concerned readers.
Eric challenges us to:
Think outside the institutional box of assumptions. Look at the Word without institutionalized glasses on. Walk by faith (God's Word) rather than by sight (what you have experienced). Allow God's Word to trump your traditions rather than the opposite. Open your eyes to see the tragedy of perpetual dependency, non-reproductive leadership, Biblical illiteracy, giving to ourselves, etc that results form the traditional form. Based on where the money goes, it is more important for you to hear 1000+ professionally prepared Bible lectures than for those who have never heard the gospel once and have no one within 2 days journey to tell them even once. This a a HUGE tragedy to the kingdom of God. Where does the Bible say you need a professional Bible lecture every week?