From this, then, it follows that as soon as the Holy Ghost, as has been said, through the Word and holy Sacraments, has begun in us this His work of regeneration and renewal, it is certain that through the power of the Holy Ghost we can and should cooperate, although still in great weakness. But this [that we cooperate] does not occur from our carnal natural powers, but from the new powers and gifts which the Holy Ghost has begun in us in conversion, 66] as St. Paul expressly and earnestly exhorts that as workers together with Him we receive not the grace of God in vain, 2 Cor. 6:1. But this is to be understood in no other way than that the converted man does good to such an extent and so long as God by His Holy Spirit rules, guides, and leads him, and that as soon as God would withdraw His gracious hand from him, he could not for a moment persevere in obedience to God.
Solid Declaration, FC 1580