Finally, the Bible says, 'Whatsoever is not of faith is sin' (Romans 14:23). This simply means we are to live out of our trust in, and dependence on, God rather than in denial of, or indifference to, God. We are to make our decisions out of faith in God, not out of doubt or unbelief—John Coblentz in The Victorious Life, page 6
Indeed! One of the names for Christians is "believers!" We need to act according to that...