Here is the oration that the Church prays in the Mass and Office for the thirteenth Sunday after Pentecost:
Omnípotens sempitérne Deus, da nobis fídei, spei et caritátis augméntum: et, ut mereámur asséqui quod promíttis, fac nos amáre quod prǽcipis.
Here is my translation:
Almighty, sempiternal God, grant us an increase of faith, hope, and charity; and, that we may merit to obtain what Thou dost promise, make us to love what Thou dost command.
Here is the translation from the Divinum Officium site:
Almighty, eternal God, grant us an increase faith, hope and charity; and make us love what You command so that we may be made worthy to attain what You promise.
The theological virtue of faith is prominent in both the Epistle and the Gospel today. In the former (Gal. 3:16-22), Saint Paul contrasts the unconditional promise made to Abraham with the Law mediated to the people through Moses, concluding with these words: “But the scripture hath concluded all under sin, that the promise, by the faith of Jesus Christ, might be given to them that believe.”
The Gospel is Saint Luke’s narration of Our Lord healing the ten lepers (Luke 17:11-19). While the virtue of gratitude and the ugliness of ingratitude are most in the foreground here — the “foreigner” leper, a Samaritan, being the only one to return and render thanks — Jesus clearly notes the grateful Samaritan’s faith: “Arise, go thy way; for thy faith hath made thee whole.”
Today’s collect asks for an increase of this faith, a virtue which, like all others, admits of augmentation. It also asks for an increase of the other two theological virtues, without which faith is not meritorious.
There are two distinct petitions in the oration. First, we ask for the increase of the theological virtues; second, we ask to love what God commands so that we might attain what He promises. The two petitions interpenetrate one another. “If you love me, keep my commandments,” Our Lord said (John 14:15). For our charity to be real, we must obey the commandments. Thus, a significant transgression of those commandments by mortal sin destroys charity and sanctifying grace in our souls. By this, we forfeit any claim to the promises made to Abraham that Saint Paul mentions. By this, we forfeit all claim to the life of grace here and the life of glory hereafter.
To avoid that calamity, we ask God to give us the efficacious grace to “make us” (fac nos) love what He commands. The very long Psalm 118 is full of expressions of what we are praying for here; to cite but one example: “Behold I have loved thy commandments, O Lord; quicken me thou in thy mercy” (Psalm 118:159).