The point of initial sanctification is we are made holy in standing before God postionally 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 (past tense) in Christ Jesus..
Yet I also see progressive 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 (present tense) from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor. Hebrews 10:14 - For by one offering He has perfected forever those who are being sanctified.
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 see it. The believer possess a positional, judicial standing of righteousness in Christ and, second, a remaining need for practical, progressive holiness that becomes more and more evident in our actions, words, thoughts, attitudes, and motives.
Sanctification as an event, positional - I am set apart/made holy because of my position in Christ, I have been united with Him in His death, burial and resurrection.
Sanctification as a process - I am progressing and increasing in practical holiness/growing in grace/maturity in Christ.