With the things of the Spirit of God,
Paul is referring to the message of God’s wisdom in the crucified Christ. These things cannot be understood by the natural person.
With the phrase natural person,
Paul is referring to the person who does not have the Spirit. In Jude 1:19 the same expression is used and then clarified with the words devoid of the Spirit.
14 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.