BY GOD'S GRACE.
I'm always surprised when RCs don't understand basic Christianity 101.
RCs - read Ephesians 1 and 2, and pray the Holy Spirit renews your mind to understand the words of God...
"For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him." -- 2 Corinthians 5:21
Seems pretty clear. And something we need to be thanking God for every day of our lives.
They would rather believe they can have the righteousness of Mary and the saints from the “treasury of merit”