So it is written: “The first man Adam became a living being”[a]; the last Adam, a life-giving spirit.
1 Corinthians 15:45 NIV
At first glance 1 Corinthians 15:45 seems to contradict that Jesus is the incarnate Holy Spirit. It also seems to suggest that Jesus was initially merely a man and that God transformed Him into a spirit after His death.
However, verses 42 to 44 clarify what is meant when Jesus is described as becoming a life-giving spirit. They clarify that Paul was speaking about Jesus’ body:
42 So will it be with the resurrection of the dead. The body that is sown is perishable, it is raised imperishable; 43 it is sown in dishonor, it is raised in glory; it is sown in weakness, it is raised in power; 44 it is sown a natural body, it is raised a spiritual body.
If there is a natural body, there is also a spiritual body. 45 So it is written: “The first man Adam became a living being”[a]; the last Adam, a life-giving spirit.
1 Corinthians 15:42-45 NIV
It is clear from verses 42 to 44 that Paul is speaking regarding the physical body. He is telling us that after Jesus rose from the dead, His physical body was replaced by a new spiritual body. As far as His body was concerned, Jesus became a spirit.
Paul is encouraging us that we will also be placed into new spiritual bodies which are the same as the body that Jesus has now. Verse 49 tells us:
And just as we have borne the image of the earthly man, so shall we[a] bear the image of the heavenly man.
1 Corinthians 15:49 NIV
Paul is telling us that we will also become spirits after we die.
Therefore, verse 45 has nothing to do with Jesus’ spirit, but is referring to what happened to His body after His death.