What is the least important aspect of faith? Eyesight. God is telling us that Lot lived by sight, not by faith. Even though God saved him, the man was what we would call today "carnal." Converted, but carnal, just as Paul told the Corinthians in I Corinthians 3, "You are yet carnal." They were converted people, just as Lot was. Lot saw the beauty of the land and realized that it would produce wealth, chosing to ignore the evil that was plainly visible to anyone who cared to notice it.
