Without question our spiritual nature is the supreme gift of God to man. Why do I say the supreme gift? Because through our spirit, and only through our spirit, has God given us the opportunity to commune with Him. We need to realize that the opportunity for His indwelling presence is the primary purpose for the existence of our spirit. God actually takes up residence in our spirit as we allow Him to do so.
It may sound a bit presumptuous to say that He indwells us only as we allow it, but that is exactly the case. Because He has given us the capacity of free will, God lives within us only as an invited guest. Our spirit has been formed by God in such a way as to provide His Holy Spirit a dwelling place within our nature.(1 Corinthians 3:16: Do you not know that you are a temple of God and that the Spirit of God dwells in you?)
I’m sure you’ve heard it said that within each person there is a God-shaped vacuum which only He can fill. That place is our spirit. Without the inhabiting presence of God, our spirit is simply dead—and therefore purposeless. So in one very large sense, our spirit is the essence of our being.