Before Christ we were enslaved to sin, but that old self was buried with Christ in baptism. We were raised to newness of life, our souls washed clean! So we are called to put off that old self when we face temptations, and, instead, to put on Christ in every trial. If we know his Word down deep, that truth will rise up in us as we fight sin and temptation and will make us more like Christ.
Mature Christianity is believing what is true; it's pursuing a true knowledge of God the Father, God the Son, and God the Holy Spirit and living according to that truth; it's rejecting what is false and lovingly affirming the truth in the face of it.
Peter reminds us that Jesus has secured our faith, righteousness, grace, forgiveness, and sanctification. Grounded in this, he urges us to persevere and grow in godliness, in the completely sufficient power and grace that Christ has provided.
Sanctification is progressively being made like Christ. It is a work of grace, but one which the believe cooperates with, unlike salvation which is purely the work of God, faith and repentance being merely our response to that work. Justification is instantaneous and complete; sanctification is progressive and incomplete until we are glorified in heaven. Justification means the end of the unconquerable dominion of sin; sanctification is the gradual growth in the power and desire to obey. Biblically, our greatest enemy is sin, the flesh; it is not the devil and our circumstances, though these can introduce temptations to us. Sanctification is a work of man and requires us to renounce sin (Tit 2:11f), mortify sin (Col 3:5), and cannot be done casually. Thus, we need to recognize that because of the power of sin, even things that are biblically allowable might be for us unhelpful and lead to further temptations. These we need to remove from our lives. This fight also must be specific. Sanctification is also a work of God and requires the Holy Spirit (Phil 2:13). We are dependent upon him to understand and love God's word, to walk in obedience, and thus we need to pray regularly to be filled with the Spirit (Eph 5:18).
In the garden we see two provisions God has made for our sin. First, we see our suffering Savior, who suffered and died in our place to bear our sin and guilt—this is our justification. Second, we see the provision that God has made through prayer to help us resist temptation and sin day to day—this is our sanctification.
Jesus appeared to take away sins. This brings us great hope not only in justification – our being made right with God – but also in sanctification, as he empowers us in the battle against indwelling sin.