Unforgivable Sin

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Therefore I say to you: Every sin and blasphemy shall be forgiven men, but the blasphemy of the Spirit shall not be forgiven. And whosoever shall speak a word against the Son of man, it shall be forgiven him: but he that shall speak against the Holy Ghost, it shall not be forgiven him, neither in this world, nor in the world to come. Either make the tree good and its fruit good: or make the tree evil, and its fruit evil. For by the fruit the tree is known. O generation of vipers, how can you speak good things, whereas you are evil? for out of the abundance of the heart the mouth speaketh. A good man out of a good treasure bringeth forth good things: and an evil man out of an evil treasure bringeth forth evil things. (Matthew 12:31-35)

In considering the worst sins, there is the most important topic of the incurable or the unforgivable sin. If we consider the evil of a sin not in comparison to other sins, but in comparison to its effect on us, this singular sin must be the worst. For any other sin, one can repent it and repair it and be cleansed from it forever.

This sin is Final Impenitence (ST II-II Q 13 A 3), which in the lists discussed, is only the last in the list of sins against the Holy Ghost, as the term has two slightly different usages. But the general meaning is the singular sin against the Holy Ghost which by its nature cannot be repented by one who commits it, and thus, cannot be forgiven. The list of sins are species of this singular sort of sin. (Ibid., A 2)

This sin is incurable by its nature. As who jumps off a high place has committed their body to the act without any means of recourse, the sin of Final Impenitence is final by its nature. As with a jumper, this does not mean that another could not intervene to save them. The unforgivable sin is not unforgivable because of any limitation of God. It is possible by way of a miracle that one who is seemingly lost is given the means to repent. But this is extraordinary: and anyone who would rely on this is actually committing the same sin, as presumption would preclude repentance by one who was committed to them.

Final Impenitence refers to the final act, but obstinately remaining in sin is similar, but can be seen earlier in life, as well as opposing the known truth, and envying another's grace,despair, and the aforementioned presumption. These all deny the means of salvation by their nature in some way.

The danger for us is that we may only think of singular sins of the gravest sort, and forget that any grave sin, even ones such as a singular act such as a lie, that one has is sufficient for a total loss of grace. We already know that a single mortal sin removes Charity and Wisdom, and this is not something we know except by an examination of conscience.

One who refuses this and is obstinate in sin, envious of the good of others, resists the truth, presumes, or despairs has in fact committed this sin without any great act that one may associate with being the worst sinner. The sin is against the Holy Ghost, not against Man or Nature. The only victim is oneself. Any delay in repentance is a dangerous thing. Any moment may be one's last and how terrible it is when that act is evil. Anyone who ever makes the claim that one can rush to Confession or make some final act of penance when death is known to approach is the gravest danger, for as we are warned: the lord of that servant shall come in a day that he hopeth not, and at an hour that he knoweth not. (Matthew 24:50) The only time we ever know we have is now, and our acts now should be good always.