So Jesus goodness... is ideal, and we "appropriate" that ideality by accepting its truth?
I think what you are asking is something based more on an evangelical perspective.
"Just believe" and this causes God to put on rose-colored glasses when He looks at you, so that He is blind to you yourself and instead "sees" only Christ?
I was taught that at one time. But no, that's not what I'm actually talking about.
I believe that yes, we certainly must believe, but it's not just a mental agreeing that saves us. Even the demons "believe". They know full well who Christ is, and they fear Him. That is not "being saved" though.
No, we are actually joined to Christ in a hidden way. We become more and more like Him (God must do this for us, but we must not stop Him). We are made to be ACTUALLY like Christ, not just "looking like Him because God put on special glasses".
No, we don't "appropriate" anything. We are meant to be REALLY CHANGED and act, speak, and think like Christ would (though because we are in human bodies, we will always fight in some ways and not be as good at this as Christ Himself). But, it is not OUR EFFORTS to do this that "save" us. But we must try, so that we don't stop God's work in us. But, it is God's work in us, made possible by Christ's death, and our belief, that all together save us.
This is what the early Christians taught. (And I should also say, it is not a "finishing" that we need. Someone can learn about Christ, be converted, and die right away, without time for all that process. God can still save them.)