John Wesley on 1 John 5:16

This extends to things of the greatest importance. If any one see his brother - That is. any man. Sin a sin which is not unto death - That is, any sin but total apostasy from both the power and form of godliness. Let him ask, and God will give him life - Pardon and spiritual life, for that sinner. There is a sin unto death: I do not say that he shall pray for that - That is, let him not pray for it. A sin unto death may likewise mean, one which God has determined to punish with death.