The Sin Nature which we were born with is a result of Original Sin Gen 2:17 Gen 3:10,11.      It was crucified with Christ.     

By Faith in Christ Jesus we are Born Again - made New Spirit beings Joh 3:5 Gal 5:25.     

Your mind, emotions and body were not crucified with Christ.     You must crucify them by acts of your will.     
   → let this mind be in you - Phi 2:5
   → mortify your members - Col 3:5
   → submit yourselves to the Lord - Jam 4:7
   → resist the devil - Jam 4:7
   → present your body - Rom 12:1
   → follow peace with all men - Heb 12:14
   → have faith in the Lord - Mar 11:22
and so on.     

All the action verbs above indicate that our soul (mind, emotions and will) are not instantly perfected in the New Birth as our spirit is 1Co 2:6 Phi 3:15.     

This verse says that we have Newness Of Life but we must walk in it.     'Walk' is an action verb implying that we have to knowingly and willfully decide to let the New Spirit being manifest.     
Otherwise, it won't.     

Spirit Salvation is instantaneous.     
Soul Salvation is a process totally dependent on our will while we are in the flesh.     

At His return Jesus will finish His redemption work by translating us from corruptible to incorruptible 1Co 15:50-55.     

In the meantime, our Lord expects us to press toward the mark Phi 3:14.     

Immersion into Christ Jesus is the point of baptism.     It is not a one time event but a for-all-time state of absorption into His Holy Spirit so that He is in us and we are in Him.