6 Our Lord Jesus Christ judged that men could more readily be bound and led on to do the things that are right by kindness than by fear, and that love avails more than dread for correction. And so, when He came, being born of a Virgin, He sent forth His grace, that sin might be forgiven in baptism in order to make us more grateful to Himself. Then if we repay Him by services befitting men who are grateful, He has declared in this woman that there will be a reward for this grace itself to all men. For if He had forgiven only our original debt, He would have seemed more cautious than merciful, and more careful for our correction than magnificent in His rewards. It is only the cunning of a narrow mind that tries to entice, but it is fitting for God that those whom He has invited by grace He should lead on by increase of that grace. And so He first bestows on us a gift by baptism, and afterwards gives more abundantly to those who serve Him faithfully. So, then, the benefits of Christ are both incentives and rewards of virtue.
Source: Letters (New Advent)