I found this interesting discussion on this topic:
http://rabbibuchwald.njop.org/2005/10/24/bereishith-simchat-torah-5766-2005/.
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The mitzvah of “p’roo ur’voo” also raises several issues regarding the prevailing attitude of Judaism toward sexuality. Many Christian sects believe that humankind is tainted by the “Original Sin” that stems from the perfidious relationship of Adam and Eve in the Garden of Eden. Later in Christian history, when the celibate class gained control of the so-called “kingdom,” all sex was deemed bad, and only celibacy was considered proper. Judaism, in stark contrast, considers procreation a mitzvah. While there are many concerns regarding sexual acts performed with improper intentions, Judaism generally views sexuality as holy and pure, especially if it is founded on holiness and purity. The Talmud actually teaches that when a sexual act is performed in the spirit of holiness, G-d Himself is present.
That procreation is a foremost feature or purpose of sexuality is clear from the prohibition of onanism, which is the wanton spilling of seed. This prohibition is derived from the text that describes the death of the sons of Judah (Genesis 38) who spilled their seed, rather than consummate the sexual act with their brother’s widow, since they knew that the child would not be called by their names.This, of course, raises many difficult issues. Is having sex with a sterile or menopausal woman a waste of the male seed? Is one allowed to have sex with his pregnant wife, since the relationship can not result in the birth of a child?
The answers to these questions lie in a well-known verse that is found in Exodus 21:10, concerning the law of the Jewish maidservant. The verse states that if the master or his son betroths the Jewish maidservant, he may not treat her as a second-class wife, “Sh’ay’rah, k’soo’tah, v’oh’nah’tah lo yig’rah,” her food, her clothing and her sexual pleasure may not be diminished. From here our rabbis learn that a wife has the right to demand sexual pleasure, irrespective of whether the act can result in the birth of a child. In effect, the positive commandment of sexually pleasing one’s wife, overrides the negative commandment of wasting seed.
We see from the law of the Jewish maidservant, that not only is the sexual act a mitzvah, but providing pleasure during that act is a mitzvah, as well. Although there have been “Victorian” periods of Judaism, especially in the late 19th century, mainstream commentators all regard sexuality in Judaism as a positive force.
In Jewish life there are two ways of achieving immortality. One may achieve immortality by bearing children who follow in one’s religious and ethical path. However, not all people are fortunate enough to have children, and it is in this context that the Talmud (Sanhedrin 19b) states: “Kol ha’m'la’mayd et ben cha’vay’ro Torah…k’ee’loo y’la’doh,” anyone who teaches Torah to his neighbor’s child, it is as if he physically bore that child.
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