The unspiritual (natural) man does not receive the gifts of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned.
What Paul calls the unspiritual or natural man, is a person we would consider as having no interest in spiritual matters, a strict materialist. This would be one who accepts matter as the basis of reality and, therefore, the body as the basis of our identity. To be spiritually discerning is to be intuitively awakened to the reality of our spiritual essence.
Scientific materialism cannot conceive of the existence of the soul. Consciousness and life itself is dependent on the physical organism. The notion of consciousness surviving the death of the body is folly. It does not fit the materialistic model.
In truth, it matters not how many textbooks are written to support the materialistic model of reality. Even Einstein could see past this limited view:
“We are slowed down sound and light waves, a walking bundle of frequencies tuned into the cosmos. We are souls dressed up in sacred biochemical garments and our bodies are the instruments through which our souls play their music.”
How do we come to know this? What is our faculty of spiritual discernment? We know it by its questioning nature. I know people who are religious mainstream thinkers. They never question their religious inheritance. Why do we? Because the larger Self, the soul, stands knocking at the door of our consciousness waiting for us to open. This knocking might be interpreted as an annoyance or a disturbance. But it only wants one thing. Open the door.