Objection 1. It would seem that the justification of the ungodly is a miraculous work. For miraculous works are greater than non-miraculous. Now the justification of the ungodly is greater than the other miraculous works, as is clear from the quotation from Augustine (9). Hence the justification of the ungodly is a miraculous work.
Objection 2. Further, the movement of the will in the soul is like the natural inclination in natural things. But when God works in natural things against their inclination of their nature, it is a miraculous work, as when He gave sight to the blind or raised the dead. Now the will of the ungodly is bent on evil. Hence, since God in justifying a man moves him to good, it would seem that the justification of the ungodly is miraculous.
Objection 3. Further, as wisdom is a gift of God, so also is justice. Now it is miraculous that anyone should suddenly obtain wisdom from God without study. Therefore it is miraculous that the ungodly should be justified by God.
On the contrary, Miraculous works are beyond natural power. Now the justification of the ungodly is not beyond natural power; for Augustine says (De Praed. Sanct. v) that "to be capable of having faith and to be capable of having charity belongs to man's nature; but to have faith and charity belongs to the grace of the faithful." Therefore the justification of the ungodly is not miraculous.
I answer that, In miraculous works it is usual to find three things: the first is on the part of the active power, because they can only be performed by Divine power; and they are simply wondrous, since their cause is hidden, as stated above (I, 105, 7). And thus both the justification of the ungodly and the creation of the world, and, generally speaking, every work that can be done by God alone, is miraculous.
Secondly, in certain miraculous works it is found that the form introduced is beyond the natural power of such matter, as in the resurrection of the dead, life is above the natural power of such a body. And thus the justification of the ungodly is not miraculous, because the soul is naturally capable of grace; since from its having been made to the likeness of God, it is fit to receive God by grace, as Augustine says, in the above quotation.
Thirdly, in miraculous works something is found besides the usual and customary order of causing an effect, as when a sick man suddenly and beyond the wonted course of healing by nature or art, receives perfect health; and thus the justification of the ungodly is sometimes miraculous and sometimes not. For the common and wonted course of justification is that God moves the soul interiorly and that man is converted to God, first by an imperfect conversion, that it may afterwards become perfect; because "charity begun merits increase, and when increased merits perfection," as Augustine says (In Epist. Joan. Tract. v). Yet God sometimes moves the soul so vehemently that it reaches the perfection of justice at once, as took place in the conversion of Paul, which was accompanied at the same time by a miraculous external prostration. Hence the conversion of Paul is commemorated in the Church as miraculous.
Reply to Objection 1. Certain miraculous works, although they are less than the justification of the ungodly, as regards the good caused, are beyond the wonted order of such effects, and thus have more of the nature of a miracle.
Reply to Objection 2. It is not a miraculous work, whenever a natural thing is moved contrary to its inclination, otherwise it would be miraculous for water to be heated, or for a stone to be thrown upwards; but only whenever this takes place beyond the order of the proper cause, which naturally does this. Now no other cause save God can justify the ungodly, even as nothing save fire can heat water. Hence the justification of the ungodly by God is not miraculous in this respect.
Reply to Objection 3. A man naturally acquires wisdom and knowledge from God by his own talent and study. Hence it is miraculous when a man is made wise or learned outside this order. But a man does not naturally acquire justifying grace by his own action, but by God's. Hence there is no parity.
Source: Summa Theologica (New Advent)