The natural person does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned. (1Co 2:14 ESV)
They are darkened in their understanding, alienated from the life of God because of the ignorance that is in them, due to ctheir hardness of heart. (Eph 4:18 ESV)
In 1 Corinthians 2:14, Paul gives us another glimpse into what this deadness and hardness implies for what we are unable to do. He says, “The natural person [that is, the unregenerate person by nature] does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned.” The problem is not that the things of God are over his head intellectually. The problem is that he sees them as foolish. “He does not accept the things of the Spirit of God, for they are folly to him.” In fact, they are so foolish to him that he cannot grasp them.
Take notice that this is a moral “cannot,” not a physical “can- not.” When Paul says, “The natural person...is not able to under- stand them,” he means that the heart is so resistant to receiving them that the mind justifies the rebellion of the heart by seeing them as foolish. This rebellion is so complete that the heart re- ally cannot receive the things of the Spirit. This is real inability. But it is not a coerced inability. The unregenerate person cannot because he will not. His preferences for sin are so strong that he cannot choose good. It is a real and terrible bondage. But it is not an innocent bondage. -John Piper, Finally Alive, p. 51-52