Teaching God's word is really really important. As Matthew Sleeman recently pointed out to us at our church, you wouldn't let an untrained surgeon loose on your body - likewise we should want our Bible Teachers, who wield a much sharper sword, to be well trained and well able to use it rightly.
As I train students in mission I'm aware that their ability to handle the Bible is a very high priority. It's not everything - nothing is gained by having an army of highly-trained Bible-wielding assassins on the loose... but an army of big-hearted Spirit-filled risk-taking sovereign-God-loving servants who can give the sense and explain the meaning of God's word to themselves and others is nigh on unstoppable. They'll hold firmly to God's promises in his trustworthy message, they'll be able to speak God's words into human objections, arguments as well as using it to bring help to those in pain and heartbreak.
Mark Dever's 9Marks Ministries Newsletter is a consistently helpful resource to assist us in doing this well: 9Marks - May/June 2007
See also John Piper at Together for the Gospel: Why Expositional Preaching Is Particularly Glorifying to God MP3