Not that I have already obtained it or have already become perfect, but I press on so that I may lay hold of that for which also I was laid hold of by Christ Jesus. (Philippians 3:13)
Following "justification" by faith comes "sanctification" by faith and finally, "glorification". Our justification, sanctification, and glorification are all God's doing; For I am confident of this very thing, that He who began a good work in you will perfect it until the day of Christ Jesus. (Philippians 1:6)
As Christians, we are already perfected in our position in Christ and we are holy before Him; I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me. (Galatians 2:20) Now He is doing His sanctifying work in us, setting us apart from a sinful, unholy world and bringing our practice-- what we say, what we do, even what we think, into conformity with our eternal holy position in Christ Jesus.
Sanctification is a life long process and God instructs us to press on, forgetting about our past failures and sin, and continually reaching forward, in faith, to our final glorification in Christ; Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. (Philippians 3:13-14)
Oswald Chambers once wrote, "Our yesterdays hold broken and irreversible things for us. It is true that we have lost opportunities that will never return, but God can transform this destructive anxiety into a constructive thoughtfulness for the future. Let the past rest, but let it rest in the sweet embrace of Christ. Leave the broken, irreversible past in His hands, and step out into the invincible future with Him." Maranatha!