In practice, based on what we have learned from the Sages and the poskim, the primary way to fulfill the mitzva of ona is that the more love and pleasure shared by husband and wife, the more holy they become. This sanctity has an ascetic element in that the husband does not think about any woman other than his wife, and the wife does not think about any man other than her husband. This sanctity also has an element of self-discovery of the divine root of their souls, for when they unite lovingly and passionately, a spark of divine unity is revealed through them, giving life to them and to all the worlds.
The verse states, “Speak to the whole Israelite community and say to them, ‘You shall be holy, for I, the Lord your God, am holy’” (Vayikra 19:2). Zohar explains that God chose the Jewish people and made them a unique nation, through which His divine unity is revealed in the world. Therefore, His holiness dwells with the Jews, and He guides them in a unique way. Zohar continues:
When is a person called “one”? When a person is male and female together, sanctified with supreme holiness, and having in mind to be sanctified through sexual union…. Then a person is whole and called “one,” with no imperfections. To this end, a man must give his wife enjoyment at that time, preparing her to share a single desire with him, wherein they both have the same thing in mind. Then when they are together, then all is one, in soul and body. In soul – they cleave to one another with a single desire; in body – as we have learned, an unmarried person is like someone who has been divided in half, so when male and female unite, they become one body. Thus they become one soul and one body, and are called one person. Then the Holy One abides in this unity and implants in [the pure souls born of their union] a spirit of holiness. They are thus called God’s children. (Zohar III 81a-b).
Nevertheless, it is well known that our abilities are limited, and the body cannot reveal all the love and truth within the marital bond. If a couple’s relationship is based primarily on physical desire, presumably it will not last. Therefore, a couple must base their relationship on a spiritual foundation as well. Doing so requires some abstinence from the physical, an asceticism that makes room for the spiritual. This abstinence is achieved primarily during nidda times, as the Torah commands.
Furthermore, the mitzva of ona can take place only within the boundaries of one’s ability to give and receive pleasure properly. Sometimes a person pursuing his desires tries having relations in addition to the set times of ona, expecting that this will increase their enjoyment and devotion. Instead he senses love slipping away, the spirit dissipating, and desires becoming more superficial. If this happens, he must return to the set times established by the Sages for the mitzva of ona, in order to restore balance between body and soul, so that the couple’s love and joy can once again come to full expression through the mitzva of ona.