While sitting by his tent door in the heat of the day, Abraham meets three messengers of G-d. One of the messengers informs Abraham, “Sarah your wife shall have a son” (Bereshit 18:10), and, later, as promised, “G-d visited Sarah…And Sarah conceived and bore Abraham a son in his old age” (Bereshit 21:1-2).
By, thus, miraculously bestowing Abraham and Sarah with a son, G-d made it possible for our forefather and foremother to do their part, like no one else, in striving to fulfill the first precept of the Torah, “Be fruitful and multiply and replenish the earth” (Bereshit 1:28).
To be sure, we find put forth by our Sages (Babylonian Talmud, Yevamot 61b) and R. Joseph Caro set down in his Shulchan Arukh (Even ha-Ezer 1:5) that the fulfillment of the above precept entails the birth and raising of a male and female child. But, like Abraham and Sarah, some of us are physically not capable of producing the requisite number of offspring. In such a case, we are taught ones rahmana patre (one under duress is not held accountable for his or her actions). But, again like Abraham and Sarah, an effort must always be made.
In describing the significance of the Biblical injunction to “be fruitful and multiply”, our Sages call upon a verse in Yeshaya 45:18, “He did not create it to be a waste; He formed it to be inhabited.” It is imperative that we not let the earth go to waste. We need the means to develop the earth’s resources to allow for our continued physical sustenance and we need the means to perpetuate a satisfactory spiritual environment to permit the refinement of moral and sublime ideals that G-d has blessed us with. That means is the youth that we produce. The youth embody the renewed strength to continue the proper physical and spiritual environment that, as we get older, we are unable to do on our own; and in the ongoing act of raising our children in accordance with our ideals, we continually fortify in ourselves those ideals.
Thus, procreation of the species and its ramifications, as opposed to sexual indulgence, is encouraged. Serving to especially instill this concept in our minds, G-d sternly prohibits sexual intercourse with one’s mother-in-law or grandmother, aunt or member of the same gender, one’s daughter or grandmother, sister or sister-in-law, son or brother-in-law, as well as with any animal (Vayikra 18:6-23; Devarim 27:20-23). One’s mother-in-law, grandmother or aunt is generally of an age in which she can no longer bear children and, of course, sexual intercourse with one’s own gender or with an animal cannot possibly produce progeny. In addition, one is often in the position of supporting one’s daughter, granddaughter, sister, sister-in-law, brother-in-law and son, who are often near us, from exploitation by others; to permit ourselves sexual intercourse with these individuals could undermine that support and allow us the possibility of sexual exploitation of those whom we should be assisting against exploitation by others (see Maimonides, Moreh Nevukhim 3:49). Moreover, intercourse with the aforementioned individuals can lead to another problem – greater susceptibility to genetically transmitted diseases. After the experiments of Gregor Mendel, the father of genetic research, in the mid-19th century and later scientific research in the field of genetics, the existence of dominant and recessive traits and their combination through sexual interaction has been demonstrated (see David Kraus, Concepts in Modern Biology, pp. 319-374). Sexual intercourse with a close relative such as a grandmother, aunt, daughter, granddaughter, son or sister, whose genetic makeup tends to simulate one’s own, would result in a greater probability for a recessive defective trait’s being dormant in each of the participants and emerging in the offspring. Also, intercourse with one’s mother-in-law and her daughter or with one’s sister-in-law and her sister or with one’s brother-in-law and his brother presents a greater opportunity for a defective family trait to emerge in the offspring. Thus, sexual relations with the above tend to incline away from promoting the procreation of healthy progeny and the production of a proper physical and spiritual environment.
In light of the above, we can also better appreciate the restriction upon cohabitation with a mamzer (Devarim 23:3; Shulchan Arukh, Even Ha’Ezer 4). Being the product of a genetically precarious union, unrestricted cohabitation with such an individual can only serve to propagate the chance of genetically defective progeny.
And to further avoid the ever-present temptation of sexual indulgence, we also find that we should not gaze upon the aforementioned relatives if we intend to derive pleasure therefrom, nor may we engage our thoughts with the act of cohabitation, nor ought we look at animals in the moment of copulation nor may one agitate the genitals (see Shulchan Arukh, Even Ha’Ezer 21-23). Thus, we are compelled to discipline ourselves to control our desires and emotional urges for our ultimate greater good.
To be sure, we have physical and emotional facets to our earthly existence and the act of sexual intercourse is included among them. The Torah recognizes this and permits their outlet. However, the existence of physical and emotional phenomena and even the sanction of their outlet does not necessitate their indulgence. In the end, the physical perishes and, along with it, the emotional. If we are to have any hope of satisfying the only part of us that can remain – the spiritual – we must set priorities. We must keep the spiritual paramount and not allow the physical and emotional to envelop us. We must, consequently, regulate our physical and emotional side, and we cannot, therefore, allow the sexual desire to so overtake us that we engage in it simply for the fulfillment of that desire with little or no concern for positive spiritual, ethical or utilitarian consequences. We must exercise restraint. We must exercise discipline.