1 John 3:9 Whosoever is born of God, commmitteth not sin: for His seed abideth in him, and he can not sin, because he is born of God.
what is born again? The spirit. Jesus told Nicodemus that one must be born from the water world, AND of the spirit in order to see the Kingdom. That Kingdom will have no sin therein. No mention of purgatory to cleanse the soul (behavior mechanism of mind will and emotions) and body.
Do you have a part of ADSUM that cannot sin ... not may not sin but CANNOT sin? When one is Born Again via the Spirit, their spirit is alive forever more because eternal life is abiding in their spirit ... soon to have a brand new body and behavior mechanism created in a supernatural event called The Departure in The Word of God.
You missed:”He who commits sin is of the devil, for the devil has sinned from the beginning.” 8
So if one sins then there is spiritual death, a separation from God caused by sin. It requires action by us: repentance, confession, penance and forgiveness in the Sacrament of Confession.
Christ death on the cross did not forgive our future sins.