Objection 1. It would seem that the excellence of the person sinning does not aggravate the sin. For man becomes great chiefly by cleaving to God, according to Sirach 25:13: "How great is he that findeth wisdom and knowledge! but there is none above him that feareth the Lord." Now the more a man cleaves to God, the less is a sin imputed to him: for it is written (2 Chronicles 30:18-19): "The Lord Who is good will show mercy to all them, who with their whole heart seek the Lord the God of their fathers; and will not impute it to them that they are not sanctified." Therefore a sin is not aggravated by the excellence of the person sinning.
Objection 2. Further, "there is no respect of persons with God" (Romans 2:11). Therefore He does not punish one man more than another, for one and the same sin. Therefore a sin is not aggravated by the excellence of the person sinning.
Objection 3. Further, no one should reap disadvantage from good. But he would, if his action were the more blameworthy on account of his goodness. Therefore a sin is not aggravated by reason of the excellence of the person sinning.
On the contrary, Isidore says (De Summo Bono ii, 18): "A sin is deemed so much the more grievous as the sinner is held to be a more excellent person."
I answer that, Sin is twofold. There is a sin which takes us unawares on account of the weakness of human nature: and such like sins are less imputable to one who is more virtuous, because he is less negligent in checking those sins, which nevertheless human weakness does not allow us to escape altogether. But there are other sins which proceed from deliberation: and these sins are all the more imputed to man according as he is more excellent. Four reasons may be assigned for this. First, because a more excellent person, e.g. one who excels in knowledge and virtue, can more easily resist sin; hence Our Lord said (Luke 12:47) that the "servant who knew the will of his lord... and did it not... shall be beaten with many stripes." Secondly, on account of ingratitude, because every good in which a man excels, is a gift of God, to Whom man is ungrateful when he sins: and in this respect any excellence, even in temporal goods, aggravates a sin, according to Wisdom 6:7: "The mighty shall be mightily tormented." Thirdly, on account of the sinful act being specially inconsistent with the excellence of the person sinning: for instance, if a prince were to violate justice, whereas he is set up as the guardian of justice, or if a priest were to be a fornicator, whereas he has taken the vow of chastity. Fourthly, on account of the example or scandal; because, as Gregory says (Pastor. i, 2): "Sin becomes much more scandalous, when the sinner is honored for his position": and the sins of the great are much more notorious and men are wont to bear them with more indignation.
Reply to Objection 1. The passage quoted alludes to those things which are done negligently when we are taken unawares through human weakness.
Reply to Objection 2. God does not respect persons in punishing the great more severely, because their excellence conduces to the gravity of their sin, as stated.
Reply to Objection 3. The man who excels in anything reaps disadvantage, not from the good which he has, but from his abuse thereof.
Source: Summa Theologica (New Advent)