The Apostle Paul isn’t saying that believers become perfect, living above sin. No. He’s talking about our growth in the Lord, being united in the faith, changed by our knowledge of Christ, and becoming spiritually mature.
We mature in the fulness of Christ by daily feeding on the Word of God, growing in knowledge and wisdom, graduating from the milk of the Word to the meat it offers.
As we walk with the Lord, facing trials, temptations, and storms; we gain wisdom and that helps mature us spiritually, to become more like Jesus. That should be the goal and desire of every believer, to be conformed to the image of Christ.