Jewish tradition does not see sex, per se, as sinful.
In fact, in the right context, and when engaged in with conscious purpose, sex is seen as a positive commandment, a force of connection—because, in contrast to food and money, sexual pleasure in itself is not connected with ownership.
It is a pleasure that is derived from giving and being connected with another—both in the body and beyond the physical plane.
It can become a most meaningful expression of love, of charity and benevolence.
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."
Strangely enough, it seems that we can learn from the birds and the beasts of the field that we are not just expressions of our physiology, that our sexuality can have aim and purpose, that we are capable of love, sharing, connection, and holiness.
Perhaps, then, looking back into the animal kingdom can help us become fully human again.
–Rabbi Adin Steinsaltz
From Simple Words, p. 107, by Rabbi Adin Steinsaltz