Catholic teaching is that our souls are truly and actually transformed by God’s grace by the power of the Holy Spirit through the merits of Jesus Christ. Some scriptures that might help you are:
"the mystery hidden from ages and from generations past. But now it has been manifested to his holy ones,to whom God chose to make known the riches of the glory of this mystery among the Gentiles; it is Christ in you, the hope for glory. (Col 1:27).
"Through these, he has bestowed on us the precious and very great promises, so that through them you may come to share in the divine nature, after escaping from the corruption that is in the world because of evil desire (2 Pet. 1:4).
“By this will we have been sanctified through the offering of the body of Jesus Christ once for all.” Heb 10:10
God is the Source of all holiness, but He freely shares His holiness with us. Holy simply means to be “set apart”. We are “set apart” when we become children of the Most High God the waters of baptism and by faith in Jesus Christ. We cannot become holy on our own, that is one of the most important things to remember. God’s grace, which makes us holy, is a gift of God that we receive with humble hearts. Catholics believe that the Holy Spirit continually sanctifies us throughout our Christian life. Becoming holy is not a one time event as some Christians believe, but an ongoing process. The Blessed Virgin is an exception to this because she was sanctified from conception in preparation for her role as the Savior’s mother. The Pope is like one of us in the sense that he is a sinner too and continues to be sanctified throughout his life.