Objection 1. It seems that the innocent is more bound to give thanks to God than the penitent. For the greater the gift one has received from God, the more one is bound to give Him thanks. Now the gift of innocence is greater than that of justice restored. Therefore it seems that the innocent is more bound to give thanks to God than the penitent.
Objection 2. Further, a man owes love to his benefactor just as he owes him gratitude. Now Augustine says (Confess. ii): "What man, weighing his own infirmity, would dare to ascribe his purity and innocence to his own strength; that so he should love Thee the less, as if he had less needed Thy mercy, whereby Thou remittest sins to those that turn to Thee?" And farther on he says: "And for this let him love Thee as much, yea and more, since by Whom he sees me to have been recovered from such deep torpor of sin, by Him he sees himself to have been from the like torpor of sin preserved." Therefore the innocent is also more bound to give thanks than the penitent.
Objection 3. Further, the more a gratuitous favor is continuous, the greater the thanksgiving due for it. Now the favor of divine grace is more continuous in the innocent than in the penitent. For Augustine says (Confess. iii): "To Thy grace I ascribe it, and to Thy mercy, that Thou hast melted away my sins as it were ice. To Thy grace I ascribe also whatsoever I have not done of evil; for what might I not have done?... Yea, all I confess to have been forgiven me, both what evils I committed by my own wilfulness, and what by Thy guidance committed not." Therefore the innocent is more bound to give thanks than the penitent.
On the contrary, It is written (Luke 7:43): "To whom more is forgiven, he loveth more [Vulgate: 'To whom less is forgiven, he loveth less' Luke 7:47." Therefore for the same reason he is bound to greater thanksgiving.
I answer that, Thanksgiving [gratiarum actio] in the recipient corresponds to the favor [gratia] of the giver: so that when there is greater favor on the part of the giver, greater thanks are due on the part of the recipient. Now a favor is something bestowed "gratis": wherefore on the part of the giver the favor may be greater on two counts. First, owing to the quantity of the thing given: and in this way the innocent owes greater thanksgiving, because he receives a greater gift from God, also, absolutely speaking, a more continuous gift, other things being equal. Secondly, a favor may be said to be greater, because it is given more gratuitously; and in this sense the penitent is more bound to give thanks than the innocent, because what he receives from God is more gratuitously given: since, whereas he was deserving of punishment, he has received grace. Wherefore, although the gift bestowed on the innocent is, considered absolutely, greater, yet the gift bestowed on the penitent is greater in relation to him: even as a small gift bestowed on a poor man is greater to him than a great gift is to a rich man. And since actions are about singulars, in matters of action, we have to take note of what is such here and now, rather than of what is such absolutely, as the Philosopher observes (Ethic. iii) in treating of the voluntary and the involuntary.
This suffices for the Replies to the Objections.
Source: Summa Theologica (New Advent)