1 Corinthians 2:14

‘Now the natural man (man in Adam, the animal man, the man of this world, the man without the Spirit, man as he is without God) does not accept the things of the Spirit of God, for they are foolishness to him, because they are spiritually discerned (examined, considered, assessed, judged).'

In contrast the ‘natural man' (‘the first man' as in Adam - 1 Corinthians 15:47) without the Spirit cannot receive them, he does not accept them because his receptors are blocked. They are dead (Ephesians 2:1). The whole stress here is that man as he is in himself is unable to receive spiritual truth, or even to consider spiritual truth. What the Spirit has taught Paul and his fellows, and is teaching through them, is nonsense to such people, for they have no spiritual discernment. It is outside their senses, outside their ability range, not mentally but spiritually. Such truth requires spiritual discernment and spiritual judgment, which can only come from the Spirit. The consequence is that it is only when the Spirit enlightens men that they can understand the Gospel, and the preaching of the cross, and respond to it. And only those who are so enlightened can go on to understand it in its fullness.