True. But if we condemn and criticize those Christians who are committing one of their mortal sins, then we must not condemn or criticize the ones that are attempting to be true to their faith.  Here is an example of Christian teachers in a Christian university who are teaching their students not to commit a mortal sin.  If we condemn the Christians that commit mortal sins, then we must also commend those who do not.  Otherwise we ourselves would be hypocrites.