My Pondering: Yes, the old passed away when faith was placed, when repentance happened, and when the baptism occurred. Yes, once and for all spiritually (that is propitiation) yet we are still living in our flesh suits, well if you are reading this and I presume you are.
So daily, we must still fight the good fight against the sinful elements in the body; like Toby Mac sings so well, “I fight the elements”. But don’t be incomplete and fight in just your own strength but get on with the spiritual armor (see Ephesians 6).
Same thing with newness. We are forever new yet daily we need to rest and abide in new mercy and grace…renewing thyself daily by practicing the divine spiritual disciplines including prayer, mediation upon the Word, reading scripture, fasting, & service.