1 John 5:16 (KJV) If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
There are two kinds of sin according to the Bible. There is sin unto death and there is sin not unto death. When a person commits sin which is not unto death, that person will be forgiven when he confesses his sin. That is the type of sin which the Bible says that when a brother sees another brother in sin, he should help the brother out of the sin.
When a person commits a sin unto death, it means that the person might not receive forgiveness. This is a dreadful thing. This is why we should live and try not to commit sin when we have given our lives to God. We should endeavor to obey the commandments of God. It is dangerous to be a christian who plays with sin. We must run away from sin and live holy.