John Paul II explores the idea that God made man and woman to be a gift to each other—their very persons, expressed through their bodies, become a gift to one another. In this chapter of the Theology of the Body, he explains what this means in more depth:
 

In the mystery of creation, the woman was “given” to the man. On his part, in receiving her as a gift in the full truth of her person and femininity, man thereby enriches her. At the same time, he too is enriched in this mutual relationship. The man is enriched not only through her, who gives him her own person and femininity, but also through the gift of himself. The man’s giving of himself, in response to that of the woman, enriches himself. It manifests the specific essence of his masculinity which, though the reality of the body and of sex, reaches the deep recesses of the “possession of self”. Thanks to this he is capable both of giving himself and of receiving the other’s gift.

 
The beauty of this gift is the mutual nature of it—the man receives the gift of the woman while simultaneously giving himself to her, and both are enriched by their giving and receiving.
 

Therefore, the man not only accepts the gift. At the same time he is received as a gift by the woman, in the revelation of the interior spiritual essence of his masculinity, together with the whole truth of his body and sex. Accepted in this way, he is enriched through this acceptance and welcoming of the gift of his own masculinity. Subsequently, this acceptance, in which the man finds himself again through the sincere gift of himself, becomes in him the source of a new and deeper enrichment of the woman. The exchange is mutual. In it the reciprocal effects of the sincere gift and of the finding oneself again are revealed and grow.

 
I am blown away when I read these truths about our very nature and contemplate that Katie and I will live this amazing mystery in our marriage, please God!