“Sanctifying grace implies a real transformation of the soul. Recall that most of the Protestant Reformers denied that a real transformation takes place. They said God doesn’t actually wipe away our sins. Our souls don’t become spotless and holy in themselves. Instead, they remain corrupted, sinful, full of sin. God merely throws a cloak (of snow over dung) over them and treats them as if they were spotless, knowing all the while that they’re not.
But that isn’t the Catholic view. We believe souls really are cleansed by an infusion of the supernatural life. Paul speaks of us as “a new creation” (2 Cor. 5:17), “created after the likeness of God in true righteousness and holiness” (Eph. 4:24). Of course, we’re still subject to temptations to sin; we still suffer the effects of Adam’s Fall in that sense (what theologians call “concupiscence”); but God removes the guilt from our souls. We may still have a tendency to sin, but God has removed the sins we have, much like a mother might wash the dirt off of a child who has a tendency to get dirty again.
Our souls don’t become something other than souls when God cleanses them and pours his grace into them (what the Bible refers to as “infused” [“poured”] grace, cf. Acts 10:45, Rom. 5:5 Titus 3:5–7); they don’t cease to be what they were before. When grace elevates nature, our intellects are given the new power of faith, something they don’t have at the merely natural level. Our wills are given the new powers of hope and charity, things also absent at the merely natural level.”