20 God gave room to Israel to enlarge its heathenism in the wide desert; whom God cut short with whetted sword, that their idolatry might not be spread abroad among the Gentiles. So our Lord allowed the Pharisee to imagine perverse things, that He might in turn duly reprove his pride. For concerning those things which the sinful woman was doing rightly, the Pharisee was thinking wrongly. But our Lord in His turn rebuked him, concerning the right things which he had wrongly withheld: I entered your house; you gave Me no water for My feet.
Behold the withholding of that which was due! But she has moistened them with her tears. Behold the payment of what was due! You did not anoint Me with oil. Behold the token of neglect! But she has anointed My feel with sweet ointment. Behold the sign of zeal! You did not kiss Me. Behold the testimony of enmity! But she has not ceased to kiss My feet. Behold the sign of love! So then, by this enumeration our Lord showed that the Pharisee owed Him all those things and had withheld them; but that the sinful woman had come in and rendered all those things which he had withheld. Because then she had paid the debts of him who wrongfully withheld them, the Just One forgave her, her own debt, even her sins.
Source: On Our Lord (New Advent)