Why can't an unbeliever know the things of God?
An unbeliever cannot know the things of God because, as the natural man, he does not receive the things of the Spirit. They are foolishness to him, he does not want them, and they are spiritually discerned, so deep doctrine and end-time prophecy remain a closed book to him.
Les explains that believers can understand and compare Scripture with Scripture, but the unsaved person cannot see how these things connect. Paul calls the unsaved person the natural man, who receiveth not the things of the Spirit of God. The unbeliever may grasp a few surface things, like the story of Bethlehem, but the deep doctrinal aspects of the Word of God and end-time prophecies are a closed book to him. Since it is all foolishness to him, he cannot know them because these things are spiritually discerned or understood.
But the natural man 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.