Transplant Surgery

"And I will give you a new heart, and I will put a new spirit in you. I will take out your stony, stubborn heart and give you a tender, responsive heart. And I will put my Spirit in you so that you will follow my decrees and be careful to obey my regulations" ~ Ezekiel 36: 26-27

It is not that we have a reconditioned heart or even that our old self is being changed. No, when we accepted Christ into our lives, we were given a whole new heart - a new self - that replaced the old, sinful nature.  While the old is seperated from us, it does still attempt to influence (sometimes, quite successfully) and regain control, but it is no longer actually a part of us.  After all, you would not pour good, fresh milk into a pitcher with old, sour milk in it - no, you would remove the old first.  The sour milk cannot be made into fresh milk any more than our old nature can be changed into something good and pure.

"Therefore, if anyone is in Christ, the new creation has come: The old has gone" ~ 2 Cor. 5:17

Does that mean we are instantly changed?  Yes, and no.

Yes, of course we are instantly changed, since God - via the Holy Spirit - swaps out our old heart/nature for the new creation.  Obviously this creates a very instantaneous change within us.  Consider this:  the "you" that exists in this world, right now (if you  indeed have the Spirit within you), did not exist in this world prior to the moment of your salvation.

No, though, is due to the fact that our way of thinking and acting was totally formed by the old - the portion now apart from us - so we have all those ways ingrained within us. 

So, while we are indeed a whole new creation, we do not necessarily act like it with the old continuing to push influence on us from without (attempting to force us to conform) and we, ourselves, giving in to it far more often than we should (we do not have to at all - ever).

"Do not conform to the pattern of this world, but be transformed by the renewing of your mind." ~ Romans 12:2  

So while we "are" instantly changed into someone/something all new, it does take us some time living as that new creation in order for us start acting like it, and that "living" is not a totally passive thing.  Some things do just seem to "happen" or "change", but much of the time, we must choose to not listen to the old and to instead, listen to the new. The more often we choose the old, the more often the old will win in our lives - like any habit, the more we do it, the easier it becomes to not only continue in, but the more we actually desire it. Remember, the old fights against the new - the two are, in a very real way, at war with each other (Galatians 5:17).

Thus - even though we are made new, it is up to us to choose which one we will listen to and allow to have control:  the new creation who desires to follow the Spirit, or the old, who wants to lead you as far away from Jesus as it can.

Do not know about you, I would rather be walking hand in hand with Jesus than with some icky, shadowy thing anyday.