“But the natural man does not receive the things of the Spirit of God, for they are foolishness to him; nor can he know them, because they are spiritually discerned” (1 Corinthians 2:14 NKJV)

The “natural” person is one who has not been born again spiritually. They are unregenerate and already dead in their sins. That is to say, they are spiritually dead. And so, they are dead to the things of the Spirit. Their spiritual deadness accounts for their spiritual deafness and blindness. Only being raised to new life will open their ears and eyes to understand spiritual things. No amount of argument or persuasion will wake the dead. Only the saving power of God’s gospel of grace received through faith will bring them to life.