Futility of mind is when a man is forever and always trying to figure out how to be happy, while he is an enemy of God. Futility is the way of the world; they are full of thoughts that are empty, vain, and useless. Yet as Christians we are to put away futility of mind as Paul says in Ephesians 4:17, "you must no longer walk as the Gentiles do, in the futility of their minds."