Sanctification has no bearing on justification. That is, even if we don’t live a sinless, perfect life 24/7 (which we won't) we are still justified by faith. (Romans 5:1) Sanctification is the process of being set apart for God’s work and being conformed to the image of Christ. This conforming to Christ involves the work of the person, but it is still God working in the believer (Philippians 2:13) who has been justified.
We see initial sanctification in which we are
set apart/made holy in standing before God positionally in Christ. 1 Corinthians 6:11 - Such were some of you; but you were washed, but you were
sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.
1 Corinthians 1:2 - To the church of God, which is at Corinth, to those who
have been sanctified in Christ Jesus.
Yet we also see progressive or ongoing sanctification in which the reality of that holiness becomes more and more evident in our actions, words, thoughts, attitudes, and motives.
1 Thessalonians 4:3-4, - For this is the will of God, your
sanctification: that you
should abstain from sexual immorality; that each of you should know how to possess his own vessel in
sanctification and honor.
So, becoming
washed, sanctified and justified in Christ is a one-time event, yet abstaining from sexual immorality is not a one-time event. Here is how I understand it. The believer possesses a positional, judicial standing of righteousness in Christ and, second, an ongoing process of growth in practical, progressive holiness which becomes increasingly evident in our actions, words, thoughts, attitudes, and motives.