1 Corinthians 15:46 However, the spiritual is not first, but the natural, and afterward the spiritual.
Our physical bodies have to have life breathed into them to start us going. God created us so that when we are born the body starts into motion and does not stop until the physical body dies.
Our spiritual bodies have to grow as well, being given life through our accepting Christ into our lives.
We can use our physical bodies to gather spiritual food so that when we do die, our spiritual selves can take on the meaning of life for us and live with God.
We need to make sure our spiritual bodies are fed enough whilst we can because we will be living that spiritual life for a long time.