Sexual desire, possibly the most powerful human desire, can become an expression of holiness.
The physical union enhances the spiritual union of two individuals.
More than that, the particular bond between male and female, in which giving and receiving blend with each other, becomes a way of learning and experiencing a multilevel connection.
In a nonabstract form, it becomes a paradigm for doing good deeds.
Study and prayer, as well as charity, may also acquire some kind of erotic fervor.
This is the reason why Kabbalistic literature describes any kind of deep connection between spiritual entities with the term "copulation."
–Rabbi Adin Steinsaltz
From Simple Words by Rabbi Adin Steinsaltz