Sanctification

"All perfectionism is essentially a disastrous misunderstanding of how God works in sanctification. Sanctification is a process by which God—working in believers through the Holy Spirit—gradually moves them toward Christlikeness (2 Corinthians 3:18). That the transformation is gradual—not instantaneous, and never complete in this lifetime—is confirmed by many passages of Scripture.

As we noted earlier, Paul wrote near the end of his ministry that he was not yet perfect (Philippians 3:12). He told the Romans, "Be [constantly being] transformed by the renewing of your mind" (Romans 12:2). And to the Galatians he wrote that he labored with them "until Christ is formed in you" (Galatians 4:19). Sanctification will not end "until we all attain to the unity of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ" (Ephesians 4:13). He urged them to stop being children, susceptible to error and trends. How were they to do that? By seeking a sudden experience? No, he wrote, "Grow up in all aspects into Him, who is the head, even Christ" (Ephesians 4:14‑15, emphasis added).

Likewise Peter instructed believers to "grow in the grace and knowledge of our Lord and Savior Jesus Christ" (2 Peter 3:18). He wrote, "Like newborn babies, long for the pure milk of the word, so that by it you may grow in respect to salvation" (1 Peter 2:2)."
                 -  John MacArthur