The “natural man,” claimed Paul under inspiration of God, “receiveth not the things of the Spirit of God, for they are foolishness unto him. Neither can he know them, because they are spiritually discerned.” (1 Corinthians 2:14)
The apostle here is making the unmistakable assertion that it is impossible for even the most rational of men to receive the things of God apart from God’s Spirit.
Left only to his natural understanding, man is incapable of discovering spiritual truth. The matter is one not just of objective inscripturated revelation, but also of spiritual discernment.