1Co 2:14 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.
Spiritual understanding has nothing to do with mans logical analytical mind. The natural man along with his physical brain thinks the things of the Spirit of God is complete foolishness, because they are only spiritually understood with the heart!
Rom 10:9 because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.
Rom 10:10 For with the heart one believes and is justified, and with the mouth one confesses and is saved.