Can spiritual teaching and keeping prevent a believer from falling into sin?
Spiritual teaching and spiritual keeping can help prevent a believer from falling into sin, but they do not make it impossible. Every human being is just as prone to fall into sin as the next one, so it can happen to anybody, and even church leaders may be taken in a great sin.
Les explains Galatians 6:1, where if a man is taken in a fall, those who are spiritual should restore such a one in the spirit of meekness, lest even the church leaders be taken in just as great a sin. He emphasizes that we are all human, and every human being is just as prone to fall into sin as the next one. Hopefully, if we are spiritually taught and spiritually kept, these things won't happen—but it can happen to anybody. Les then turns to John's delineation: some sins do not cause God to take a believer out of physical life, but some He will. A believer who refuses to come away from his sinful lifestyle may face a sudden death—heart attack or car accident—because God takes them home lest they keep bringing reproach to His name. This is the sin unto death, and no believer or church body has the right to pray for the death of an erring believer; that is in God's hands.