Within my body, I have a complete nervous system, digestive system, circulatory system, respiratory system, etc. These systems sustain and benefit my own bodily life. But what about the reproductive system?
The reproductive system is only complete when joined with another’s, and it exists for the creation of yet a third.
The reproductive system points to the truth that we are not made for ourselves. We are made to give ourselves away: we are made for love.
(For much, much more along these lines, see Pope St. John Paul II’s Theology of the Body. I started with Theology of the Body for Beginners by Christopher West.)