I just heard a great line from a Rob Bell sermon. The biblical idea of maturity is "complete; lacking nothing."
"Spiritual maturity is when you do the right thing with or without the accompanying feelings and thoughts."
Or to rephrase it, "Spiritual maturity is when your convictions and beliefs trump your thoughts and feelings."
Or to use another picture, "It's when your beliefs and convictions drive the bus and tell your thoughts and feelings, 'you sit here!';"
Rob admitted that none of us are completely mature. "Spiritual growth is closing the gap."