The fact that David said this first is instructive. It tells me that this is something that is not just a messianic reference, though it certainly is, but it is a reference as to how David chose to live, a life with his spirit committed to the Lord.
It occurs to me that David’s choice is a great model. What would it look like if all of us that clam to follow Christ lived life with our spirit committed to Christ? In reality that is the case. If we have trusted Him our spirit is His, alive in Him. But, my observation of both my life and the life of some of those around me is that I do not live that way consistently.
What if we did?