If you are saved, you have received the spirit which is of God; that we may know the things that are freely given to us of God." 1 Cor. 2:12.
The natural man (the unsaved man) uses human reasoning for his discernment. "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." 1 Cor. 2:14.
Man, saved or not, is a composite of body and soul. Potters clay infused with a spirit. When you read the Bible you do so with fleshly eyes even though it is the inner eye that “sees” the truth. When you speak to others it is with a fleshly tongue that communicates what you know to others.