1 John 5:16

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.

Ver. 16. A sin which is not unto death] When John Frith and Andrew Hewer were at the stake, Dr Cook openly admonished all the people that they should in no wise pray for them, no more than they would do for a dog at which words Frith, smiling, desired the Lord to forgive him. (Acts and Mon. fol. 946.) In its own nature all sin is mortal; but in a saint being tempered with faith and repentance, it is as quicksilver tempered with ointment and killed.

There is a sin unto death] That unpardonable sin of doing despite to the Spirit of grace. Rockwood, a chief persecutor at Calais in the days of Henry VIII, to his last breath, staring and raging, cried, He was utterly damned; and being willed to ask God mercy, he brayed and cried out, "All too late! for I have sought maliciously the deaths of a number of the most honest men in the town, whom I knew to be so; all too late, therefore, all too late." Another that had committed this sin to death, wished that his wife and children and all the world might be damned together with him. (Mr Burroughs' Mos. Choice.)