At this point, John Paul II is still talking about the creation of man as laid out in Genesis, and the appeal of Christ to those words.
Man was created as male and female, and it is significant that there are two separate accounts which each tell us different things about this important aspect of mankind. Christ refers to both of these when he appeals to "the beginning".
When we examine the second creation story in detail, and in relation to the first, we note a certain richness that is expressed there. In this story, God created man (Adam) first, but man was alone. Though similar to the beasts, because he possessed a body, Man was different from them in significant ways. He could make choices, he was in the image of God.
Adam was the first man, or properly the first Human. In him was embodied all that is humanity. But, it is not good for man to be alone, so God created the animals, which didn't change the solitude that Man existed in, to this point. And so, God put Adam into a deep slumber (removing the will of Adam from the equation) and fashioned woman from the rib of Adam.
It was not until this point that Adam had any sense of "maleness" because an understanding of sex (gender) cannot exist without the complimentary relation between male and female. And so, up until the creation of Eve, Adam and Eve were literally and actually one flesh. And so, when it is said that through conjugal union, the two will become one flesh, this is what it meant by that. Adam, being the archetypal human, is complete in all ways. This completeness is what is reached when "the two become one flesh" through the conjugal union.
When they unite with each other (in the conjugal act) so closely so as to become "one flesh," man and woman rediscover every time and in a special way the mystery of creation, thus returning to the union in humanity ("flesh from my flesh and bone from my bones") that allows them to recognize each other reciprocally and to call each other by name, as they did the first time. ... The fact that they become "one flesh" is a powerful bond established by the Creator through which they discover their own humanity, both in its original unity and in the duality of a mysterious reciprocal attraction. (TOB 10:2)Man is not truly complete as only male or only female, but regains a fullness in humanity through the community of persons, the relations between male and female.
I look forward to continuing these discourses.