Sanctification is a process.
Justification is immediate and is totally from God.
What makes us be a new creation?
Are we one immediately upon justification?
Sanctify means to set apart, to prepare, make ready, for the work of God.
Does a person that has just been saved even understand what God may want of them?
Sanctification, being set apart for God's work, is a life-long process.
1 Peter 1:15-16 is akin to Mathew 5:48
Be perfect
Be holy
It is a desire, a working toward; we are neither perfect nor completely holy, but it is our desire--something to work for.
Romans 12:1
2 Peter 3:18
1 Peter 2:2-3
2 Corinthians 7:1
Philippians 2:12-13
and many more
Everything is immediate with God.
When and [if] we are born again of the spirit of God, that new creation is new in us, but eternal in God. We do not walk in darkness any longer, not one bit, but in the light, for God is with us. With God there is no beginning and no end - this is that new creation, and therefore it is not a process having a beginning and an end, as the things of the flesh and of the world. It just seems that way, because we are prone not to put away (to kill) the the flesh and the old man. But by the spirit of God, we serve Him in spirit forever, even if He is stifled by our old self.
Also, Peter and much of what is written during those times, is written to and for many who were not born again of the spirit during this life, but died in there sins, only to be saved in the death they shared with Christ on the cross, with Christ whom is the Last of those born of the flesh and of the fallen. This is why we are told that we are adopted into Israel, for we too are first born of the flesh, but adopted into Israel - not in this life, but in the same death.
The cross is the apex of all things, the only process, bringing silence in heaven for half an hour...that is all. Therefore, He said, "
It is finished."