Such a person may not actually be a believer, but there is also the possibility he is. Actions don’t always follow beliefs. As unfortunate as it is, there are those who have sincerely trusted Jesus Christ as their personal Savior who are not living like it. It is often for one of two reasons.
One is that they have never grown as a Christian. Instead they are what Hebrews calls, “babes” (5:13) As we grow as Christians, God uses the Scriptures to take out of our lives what should not be there and put in what should. There are sins we need to confess, temptations we need to avoid, and weaknesses we need to overcome. God in His grace and through the Scriptures reveals those to us. If we are not studying the Scriptures, though, we are without the instrument God uses to point those things out. We are again what Hebrews calls, “unskilled in the word of righteousness” (5:13).
A second reason may be that just as children can walk away from a human parent, Christians can walk away from the Lord. In so doing, they can be disobedient to Him and live lives that cause non-Christians to say, “I live a better life than they do.”
In I Corinthians 5, a Christian was committing immorality with his father’s wife. In I Corinthians 6, Christians were going to court against each other. In I Corinthians 11, Christians were dishonoring the Lord at what was called the Lord’s supper. If you had watched their lives at those particular moments, you would have had reason to wonder if they actually knew the Lord. Yet the Scriptures do not deny the fact that these people were believers.
Any believer who has sincerely trusted Christ and is not living like it, should fall to his knees and ask the Lord for forgiveness and help in changing his behavior. God wants every Christian to live a life that attracts people to the Savior not turns their attention away from Him.