St. John Chrysostom commenting on the biblical story of Cain murdering his brother Abel, sees in Cain’s lament of Genesis 4:13-14, Cain belatedly repenting of his misdeed. Cain only repents when he is confronted with his punishment, but by then it is too late for his repentance to make a difference. Chrysostom sees in this a lesson for us all: God promises to forgive our sins, but doesn’t promise us a tomorrow on which to repent.
“Cain said: ‘My guilt is too great for me to be forgiven.’ Behold the complete confession. In other words, such is the sin committed by me, he is saying, that I cannot be pardoned. Someone may say, Behold he has confessed, and confessed with great precision – but all to no avail, dearly beloved: the confession comes too late. You see, he should have done this at the right time when he was in a position to find mercy from the Judge. Remember now, I ask you, what I was saying a short time ago, that on that dread day and before that impartial tribunal each of us will repent our sins, seeing before our eyes those fearful punishments and the ineluctable chastisements – but all to no purpose, as we have run out of time. In other words, it is before punishment is imposed that penance is appropriate and is so marvelously efficacious. Hence I beseech you, when this remarkable remedy is able to take effect, let us then take advantage of it, and while we are still in this life let us apply the healing power coming from repentance; and let us learn for sure that it will be of no avail to us to repent after the show is over and the time for the contest has passed. Let us, however, return to our theme. you see, when Cain was asked by the Lord, ‘Where is your brother Abel?’ that was the time for him to confess his fault, fall on his knees, pray and ask pardon. At that point, however, he rejected the healing, whereas not, after the sentence, after all was over, after the accusation was leveled at him in a loud voice by the blood that had been shed, he made his confession to gain nothing from it.” (St. John Chrysostom in Homilies on Genesis 18-45, pg. 29)