In his discussion of the tumah, or spiritual impurity, which is imparted to males as a result of various bodily excretions, Abarbanel is puzzled by the fact that the concept of tumah is also associated with the emission of semen. The Torah tells us that when a man and woman have marital relations they must immerse in a mikveh, or ritual bath, and remain in a state of tumah until evening. How can it be that an act which is one of the most important mitzvot of the Torah — both from the perspective of reproduction and the perspective of man’s responsibility to fulfill the needs of his wife — result in a state of spiritual impurity?
Abarbanel answers that, in general, bodily secretions whose elimination is not necessary for the health of the individual create a state of tumah. This explains why the elimination of feces, urine, mucus and saliva does not create a state of tumah. The elimination of seminal fluid, however, is not necessary for bodily health, and as a result does result in a form of spiritual impurity. In this case, the state of tumah is also a result of the Torah’s desire to establish reasonable parameters for marital activity. As holy, natural and important as this activity is, we must always be reminded that we must be the masters of our physical desires rather than being slaves to them. Abarbanel is saying that by imposing this limitation the Torah is preventing us from engaging in the kind of activity that characterizes the immoral behavior of people like adulterers who give themselves over totally to their physical desires. However, because of this importance, the duration of the state of tumah is limited to one day, and there is no required sacrificial offering, unlike other situations where the duration of tumah is seven days with a required sacrificial offering.