In Judaism, sex is never looked on as something wrong or shameful.
It is, on the contrary, considered to be a high level of action potentially capable of bringing out the noblest attributes, not only in the realm of individual feeling, but also in the realm of holiness.
And it is nevertheless precisely because of this potential that strict restraints are called for.
Indeed, the whole order of relations among the various worlds may be conceived in images of intimate engagement, a kind of sexual contact between one world and another, between one level of being and another.
That is why sexual relations themselves have an enormous influence on the soul.
All this, besides their primary power-to create a new human being-makes it clear why it is necessary to be extremely respectful to and solicitous about all that concerns the use of the power of sex.
In principle, Judaism does not see sexuality only as an instrument for the propagation of the human race, a means of being fruitful and multiplying.
The relations between a man and a woman are an organic network, becoming an entity in itself.
It brings about the creation of another unity, the family, which is the basic cell of social existence.
More profoundly, the family unit is part of the integration of the human individual.
In other words, the unattached individual is not yet a whole person; the whole individual is always double, man and woman.
–Rabbi Adin Steinsaltz
From The Thirteen Petalled Rose by Rabbi Adin Steinsaltz