Here is the oration that the Church prays in the Mass and Office for the sixteenth Sunday after Pentecost:
Tua nos, quǽsumus, Dómine, grátia semper et prævéniat et sequátur: ac bonis opéribus iúgiter præstet esse inténtos.
Here is my translation:
Thy grace always both preceding and following us, we beg Thee, O Lord, may it also grant us to be continually intent upon good works.
Here is the translation from the Divinum Officium site:
Lord, we pray thee, that thy grace may always prevent and follow us, and make us continually to be given to all good works.
Once more, we find the Church’s doctrine of grace clearly expressed in a liturgical oration asking for that very thing: grace. There is, in theology, a division of grace into “prevenient” and “subsequent” (or “consequent”) grace. God’s actual grace both “comes before” and “follows after” our free acts. The verbs used in today’s collect (praevenīre and sequī) mean literally “to come before” and “to follow” (to “prevent” something is literally to “come before” it; a “sequence” or “sequel” is something that follows). Below, you may find a wonderful excerpt from Saint Thomas on this doctrine.
But first, another place in the Church’s lex orandi where we find the doctrine beautifully expressed is in this prayer, which is part of the ancient Litany of the Saints:
Actiones nostras, quaesumus, Domine, aspirando praeveni et adiuvando prosequere: ut cuncta oratio et operatio a te semper incipiat et per te coepta finiatur.
Which is to say, in a very free translation…
Direct, we beseech Thee, O Lord, our actions by Thy holy inspirations and carry them on by Thy gracious assistance; that every prayer and work of ours may always begin with Thee and through Thee be happily ended.
And now, here is Saint Thomas’ explanation of prevenient and subsequent grace:
…God’s grace is the outcome of His mercy. Now both are said in Psalm 58:11: “His mercy shall prevent me,” and again, Psalm 22:6: “Thy mercy will follow me.” Therefore grace is fittingly divided into prevenient and subsequent.
…As grace is divided into operating and cooperating, with regard to its diverse effects, so also is it divided into prevenient and subsequent, howsoever we consider grace. Now there are five effects of grace in us: of these, the first is, to heal the soul; the second, to desire good; the third, to carry into effect the good proposed; the fourth, to persevere in good; the fifth, to reach glory. And hence grace, inasmuch as it causes the first effect in us, is called prevenient with respect to the second, and inasmuch as it causes the second, it is called subsequent with respect to the first effect. And as one effect is posterior to this effect, and prior to that, so may grace be called prevenient and subsequent on account of the same effect viewed relatively to divers others. And this is what Augustine says (De Natura et Gratia xxxi): “It is prevenient, inasmuch as it heals, and subsequent, inasmuch as, being healed, we are strengthened; it is prevenient, inasmuch as we are called, and subsequent, inasmuch as we are glorified.”