Thomas Aquinas offers his pre-Reformation views on justification:
newadvent.org/summa/2113.htm
Highlights (not in any particular order):
"justice is so-called inasmuch as it implies a certain rectitude of order in the interior disposition of a man, in so far as what is highest in man is subject to God, and the inferior powers of the soul are subject to the superior, i.e. to the reason; and this disposition the Philosopher calls “justice metaphorically speaking”
“There are four things which are accounted to be necessary for the justification of the ungodly, viz. the infusion of grace, the movement of the free-will towards God by faith, the movement of the free-will towards sin, and the remission of sins. … in their natural order the first is the infusion of grace; the second, the free-will’s movement towards God; the third, the free-will’s movement towards sin; the fourth, the remission of sin.”
“The movement of faith is not perfect unless it is quickened by charity; hence in the justification of the ungodly, a movement of charity is infused together with the movement of faith.”
“the justification of the ungodly by God takes place in an instant.”
“the gift of grace that justifies the ungodly is greater than the gift of glory that beatifies the just, for the gift of grace exceeds the worthiness of the ungodly, who are worthy of punishment, more than the gift of glory exceeds the worthiness of the just, who by the fact of their justification are worthy of glory”