They become a one-flesh unity and I m not just talking about their bodies. When I say that I m not just talking about their bodies, I mean that at every level, male and female were designed to complete each other. In sexual self-giving, the hearts and minds and spirits of the husband and wife cooperate with their bodies. They are united not just in their bodily dimension, but in every dimension. This unity also helps prepare them to be parents, and the hope of children joins them in solidarity with every past and future generation.
Casual sex can t achieve that.
It endlessly joins and severs, joins and severs. Imagine what it would be like to repeatedly tear off and reattach your arm. It is the same when you repeatedly tear off and reattach your various sexual partners. You will have destroyed your capacity for intimacy. Many readers are mystified as to how it got into the sacred Scriptures, but the ancient rabbis had an explanation.