Augustine of Hippo, on 1John 5:16

“He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that any man ask.”

“This difference of sins it is that distinguishes Judas with his treason from Peter with his denial. Not that to him who repenteth there is to be no forgiveness: lest we go against that sentence of the Lord, in which He commands always to forgive the brother who asks his brother's forgiveness: but that the mischief of that sin is, that the man cannot submit to the humiliation of begging for pardon, even when he is forced by his evil conscience both to acknowledge and to publish his sin. For when Judas had said, "I have sinned, in that I have betrayed the innocent blood," he went and hanged himself in desperation, rather than pray for forgiveness in humiliation. Wherefore it makes a great difference, what sort of repentance God forgives. For many are much quicker than others to confess that they have sinned, and are angry with themselves in such sort that they vehemently wish they had not sinned, while yet they cannot lay down their pride, and submit to have the heart humbled and broken so as to implore pardon: a state of mind which one may well believe to be, for the greatness of their sin, a part of their already begun damnation.”

Imported from an open dataset — not yet checked against the printed edition.