“So prepare your minds for action and exercise self-control. Put all your hope in the gracious salvation that will come to you when Jesus Christ is revealed to the world. So you must live as God’s obedient children. Don’t slip back into your old ways of living to satisfy your own desires. You didn’t know any better then. But now you must be holy in everything you do, just as God who chose you is holy. For the Scriptures say, “You must be holy because I am holy.””
1 Peter 1:13-16 NLT
Once we begin to become more like Christ we start to pivot a 180 from our old selves. We just haft to stay consistent in our faith, but we’re finite beings and we slip up sometimes. Peter is noting that believers must not slip up from there obedience to God, to not slip back into our old ways of living. As Christians we’re to move forward and start the process of sanctification. It’s okay to look back and see how much God has changed you with the spirit, but don’t fantasize about the “good old days”. We can praise God for this that he’s changed our views of the world and how he’s saved us from eternal death.