This is something i realized at work the other day . . .
In the Bible, i'm not sure where, i believe it says we are 'grafted' into the Body of Christ when we receive the Holy Spirit. When Christ lives within us, He makes us one with Him, and we are no longer what we were, but rather grafted onto Him.
I want to go a little further into this; as most of you know, we have a flower/vegetable/fruit tree section at the feed store. The vast majority of the fruit trees we sell, and off the top of my head i can't think of any exceptions to this, are grafted trees. The rootstock has to be a hardy plant that's climatized to the area, and can endure the heat, the drastic changes from one day to the next, the droughts, etc. What that does is it sets the foundation for what's grafted onto it, so that its immunities and ability to endure is passed on to what is to be grafted. The rootstock pretty much surrenders what it naturally is so that something else can thrive as it would have.
Here's a brief summary of how to graft a tree; when the rootstock is still a young tree, it must be cut off about a foot or so from the ground. It is then split a few inches down the middle. A branch of the weaker tree, the one that would otherwise be fruitless, is usually (not always) dipped in a hormone that encourages root growth, then set down in the split of the rootstock, and then it's tied together so the rootstock can grow over the grafted branch and make the two into one . . .
The rootstock gives what is rightfully its own in exchange for the sake of the weak, barren and fruitless. It is cut off so that another plant, one that, if all was fair, would not be able to grow (or, if it did, it wouldn't produce fruit). The grace shown by the rootstock covers the faults of the grafted branch.
Not only this, there are trees that are grown in nurseries for the sole reason of being cut off so that the weak, frail tree could grow.
Jesus must be our rootstock. He was born to be cut off so that we could be grafted onto Him, so that He could grant us the life that we would otherwise not have, so that our branches may produce fruit. If we give ourselves to His sacrifice, and tie ourselves to Him, He will grow around us, and He will change us into something new.
He will root us in the spiritual, and grant us life in a place we could never dream of existing. We were made for Heaven, but humanity has fallen to the point that we've decided that we're born the the world.
We are unable to, on our own, produce fruit that is good.
Without a rootstock, our roots will rot and our fruit become bitter, or nonexistent at all. Being rooted in Christ through His sacrifice gives us the ability to, once again, produce a fruit that will satisfy, a fruit that will not rot or be bitter or unpleasant.
It allows us to be what we were made to be.