Thomas Aquinas

“ Reply to Objection 2: Since a man cannot prepare himself for grace unless God prevent and move him to good, it is of no account whether anyone arrive at perfect preparation instantaneously, or step by step. ”

“ An agent of infinite power needs no matter or disposition of matter, brought about by the action of something else; and yet, looking to the condition of the thing caused, it must cause, in the thing caused, both the matter and the due disposition for the form. So likewise, when God infuses grace into a soul, no preparation is required which He Himself does not bring about. ”

“ But however much the clay is prepared, it does not necessarily receive its shape from the potter. Hence, however much a man prepares himself, he does not necessarily receive grace from God.
I answer that, As stated above (A [2] ) , man's preparation for grace is from God, as Mover, and from the free-will, as moved. Hence the preparation may be looked at in two ways: first, as it is from free-will, and thus there is no necessity that it should obtain grace, since the gift of grace exceeds every preparation of human power. ”

“ It is an essential condition of knowledge that a man should have certitude of the objects of knowledge; and again, it is an essential condition of faith that a man should be certain of the things of faith, and this, because certitude belongs to the perfection of the intellect, wherein these gifts exist. Hence, whoever has knowledge or faith is certain that he has them. But it is otherwise with grace and charity and such like, which perfect the appetitive faculty.
Reply to Objection 3: Sin has for its principal object commutable good, which is known to us. ”

“ Now an instrument does not bring forth the action of the principal agent by its own power, but in virtue of the principal agent. Hence Christ's humanity does not cause grace by its own power, but by virtue of the Divine Nature joined to it, whereby the actions of Christ's humanity are saving actions. ”

“ Further, as knowledge is a gift of God, so is grace. But whoever receives knowledge from God, knows that he has knowledge, according to Wis. 7:17: The Lord "hath given me the true knowledge of the things that are." Hence, with equal reason, whoever receives grace from God, knows that he has grace.
Objection 3: Further, light is more knowable than darkness, since, according to the Apostle (Eph. 5:13) , "all that is made manifest is light," Now sin, which is spiritual darkness, may be known with certainty by one that is in sin. Much more, therefore, may grace, which is spiritual light, be known. ”

“ Thirdly, things are known conjecturally by signs; and thus anyone may know he has grace, when he is conscious of delighting in God, and of despising worldly things, and inasmuch as a man is not conscious of any mortal sin. ”

“ The Divine care may be looked at in two ways: first, as regards the Divine act, which is simple and uniform; and thus His care looks equally to all, since by one simple act He administers great things and little. But, "secondly," it may be considered in those things which come to be considered by the Divine care; and thus, inequality is found, inasmuch as God by His care provides greater gifts to some, and lesser gifts for others. ”

“ As in the person of Christ the humanity causes our salvation by grace, the Divine power being the principal agent, so likewise in the sacraments of the New Law, which are derived from Christ, grace is instrumentally caused by the sacraments, and principally by the power of the Holy Ghost working in the sacraments, according to Jn. ”

“ Now it sometimes happens that God moves a man to good, but not perfect good, and this preparation precedes grace. But He sometimes moves him suddenly and perfectly to good, and man receives grace suddenly, according to Jn. ”