¶ … except a man be born again, he cannot see' namely he can neither understand the nature nor share the blessedness- of the kingdom of God" can best be understood by recourse to William James's discussion on converts. A convert is a man who is born again; who perceives his 'personhood in a different way. The Personhood or ego, according to James is categorized into two aspects:

The phenomenal self (the experienced self, the 'me' self, the self as known)

The self-thought (the I-self, the self as knower).

It is the way that one perceives the world that shapes this Me/I and, in turn, this Me/I effects the way one perceives the world.

The 'I' is the constant flow of subjective thought that the person has about the self and which makes the person perceive the self, moment per moment, in a certain way

The ME self is divided into three different interrelated aspects of self:

the material self (I.e. anything in which we feel some sort of physical ownership towards such as our bodies, our families, our possessions),

the social self (our feelings of social relations),

The spiritual self (our feelings of our own subjectivity).

Whilst we may think of the 'I' as a consummate whole comprised of an indistinct past, present, future all fused together, it is in reality (according to James), a pointillist pattern made of different experiences and perceptions that occur in different points of time.

Returning to the New Testament phrase of "except a man be born again, he cannot see', we can interpret James in this way: A man who believes in a certain way for a...

The man however may be deceived; he may be delusional. In which case, his personhood is not really 'seeing' in the genuine sense of the world. It is obstructed and, unknown to himself, polluted and unclear. Given, however, that the man's perception changes (his objective 'me' changes the stream of 'I' thereby changing the self), from that moment on the man's seeing changes -- his self-changes -- since he sees the world differently. This affects the objective way he perceives himself and the world. And in turn affects the way he thinks about himself (the I). Thereby becoming, in a sense, a different person.
This was James' rendition of convert. A convert is no longer the old person. He is a totally different person for he literally sees the world in a new way -- he is, according to the New Testament, seeing it clearly for the first time -- and so now for the first time he can see.

In a similar way, Plato may also accord us some understanding.

In his famous metaphor, Plato compared the general human to someone who is fettered in a cave just seeing the shadows of the dancing fire. But he is not aware of the fact that his perceptions are contrived and false. He is only the one who managed to escape from the cave, climb outside into the air that returns to the others and exults of a reality that he has seen -- a reality outside the cave. This is the man who is born again. He has climbed out of his previous existence and gained access to a wider world and broadened vista. The shutters have fallen from his eyes, so to speak, and he sees…