unbeliever can't understand

But the natural [unbelieving] man does not accept the things [the teachings and revelations] of the Spirit of God, for they are foolishness [absurd and illogical] to him; and he is incapable of understanding them, because they are spiritually discerned and appreciated, [and he is unqualified to judge spiritual matters}

1 Cor 2:14

Berean Standard Bible

The natural man does not accept the things that come from the Spirit of God. For they are foolishness to him, and he cannot understand them, because they are spiritually discerned.