1 Corinthians 2:14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness to him: neither can he know them, because they are spiritually discerned. 

And they cannot know these things unless they are born again and come to maturity in Christ.  When a person is born again into the Kingdom of God, they have spiritual senses just as a baby who is born in the natural has natural senses.  As they mature, which is by grace and grace is through faith, their senses become more keen.  They begin to be able to recognize God because they know Him more intimately.  That is the nature of spiritual maturity.  There are many scholars of the Bible and theology who are still babies because they don't really know God.  Some of them have even become disconnected from the Head, Jesus.