Look at this way: I read a story of a young high school man who raped a girl simply because he was looking for some pleasure.
In effect, it is not simply that this young man caused the girl physical pain. For if that was all, why then have eternal physical pain?
But there is something deeper. God has created every human creature for the purpose of giving His Total Self, which is Inifinite, All-penetrating Love and Truth, to the creature, and, by the power of His created grace, to receive the supernatural love of the creature back, and for an endless duration.
It is for this reason that every human creature is priceless, immeasurable.
hence, when some other creature treats another human creature as though it is but an object to used for mere superfiical gain, and then discarded, one is insulting the worth of the creature in an INFINITE manner, for the sinning creature is consdering the worth of the human to be merely finite when it is in fact immeasurable.
hence, with an immeasurable insult, the debt is immeasurable.
Therefore, no human creature can atone for a mortal sin, seeing as the punishment for such a crime must be the counterpart, which is then unending emotional and physical torment, seeing as the victim is called to unending bliss and joy.
So only God can repay the debt by joining His Divine Essence with a created body and soul and suffering physically, emtionally, and spiritually. And because it is actually the Infinite God who does this, it has immeasurable worth.
For more info, I have an article called:
Darth Vader, Lust, and Hell
Blessings to you, Ellej!