God is “one,” and He determined that the nation of Israel would also be “one,” and that every Jewish person can cling to God through transforming into “one.” When is a person “one”? It is only when male and female join [in physical intimacy] with holy intentions. Their unity takes place with the desire of both of them, and then, when they are physically intimate, they are as one body, and then God grants them a spirit of holiness.

When is a human being called “one”? It is at the time when the male and female are physically intimate, sanctifying themselves with an elevated holiness, with the intention of sanctifying themselves. Come and see: When the human being is physically intimate as male and female and, as is appropriate, intends to sanctify himself, he is then complete, and called “one” and is without flaw. For this reason, a man has to make his wife joyous at that time, inviting her to become one with him, so both of them share this intention. When both of them are together, then all is one [they are united] in both soul and body. In soul, they cling together through their shared intentions. In body – it is, as we have learned, that an unmarried man is like one who is fragmented.

And when the male and female unite, they become one body. In this way, they are one soul and one body and are called “one person.” Then, the Holy One, blessed be He, rests upon that “one” and deposits a spirit of holiness within that one. (Zohar 3:81b)

Further reading: For more on man and woman as two parts of a whole, see p. 16.

The physical union between a man and woman is an elevated matter that the Torah refers to as “knowledge,” because it causes knowledge and wisdom to descend to the world. This union, when performed with holiness, causes the Divine Presence to dwell together with the husband and his wife. But if their physical union is only powered by physical lust, the Divine Presence removes itself from them and they are left with only fire that devours them.

The physical union between a man and his wife is referred to as “knowledge”:

Know that this union is sacred and pure when done in the proper way, at the proper time, and with the correct intentions. A person should not think that, God forbid, there is any shame or ugliness in appropriate marital intimacy. For marital intimacy is referred to as “knowledge.” It is not for naught that the verse states: “Elkana knew Chana his wife” (I Samuel 1:19). This is the inner meaning behind the drop of seed that, when drawn from a holy and pure place, draws along with it knowledge and understanding, which is the mind. Realize that if marital intimacy were not a holy matter, it would not be referred to as “knowledge.”

When marital intimacy is performed with holiness the Divine Presence is with the couple:

For the Sages, of blessed memory, said: “When a person is physically intimate with his wife in holiness and purity, the Divine Presence rests with them. But if they become lustful, the Divine Presence detaches itself from them and they remain ‘fire and fire’” (Kala Rabati 1:7). This is similar to what the Talmud teaches: “Rabbi Akiva taught: If a man and woman merit, the Divine Presence rests between them. [But if] they do not merit, fire consumes them” (Sota 17a). Both statements can be explained as follows: When the Divine Presence is between them, the yod of the word ish (alef-yod-shin) and the heh of the word isha (alef-shin-heh) are still present, and the name of God (yod-heh) is between them. But if they did not intend to have a holy union but, instead, to merely fulfill their desire, and they became fired with lust and desire, the yod of the man’s name and the heh of the woman’s name, that together form the divine name yod-heh, depart from between them and two fires (eish, alef-shin, that remains when the yod is removed from the word ish, and eish, alef-shin, that remains when the heh is removed from the word isha) remain. (Ramban, Igeret HaKodesh, chap. 2)

Further reading: For more on holy intimacy, see A Concise Guide to Halakha, p. 574.

One of the hasidim of Rabbi Moshe of Kobrin had a difficult time finding a husband for his daughter because his daughter was very exacting and kept rejecting the suggestions that were made to her. When he saw that his daughter would find fault with every boy that was suggested as a match for her, the father decided to travel to his rebbe and seek his counsel.

For a man without a wife is half a body, and the Divine Presence does not rest upon him. (Zohar 2, Behar 32)

One who truly loves another is always either afraid of doing something against his beloved’s will or afraid that something will happen to his beloved. This is what they meant by “love is full of fear.” (Rabbi Yaakov Tzvi Mecklenburg, HaKetav VehaKabbala, Genesis 22:12)

For love is the uniting of the two lovers as if they were one entity. (Rabbi Yitzĥak Arama, Akedat Yitzĥak, Genesis 2:18)

I always say to a couple at their wedding: “Take care, dear couple, to always strive to give each other satisfaction…. And know that the moment you start to make demands of one another, your bliss will evade you.” (Rabbi Eliyahu Eliezer Dessler, Mikhtav MeEliyahu, vol. 1, p. 36)

It is accepted practice that Jewish man consults with his wife in all of his affairs…both at home and outside the home. This is so that a wife should know about all of her husband’s affairs and advise him about them, both at home and in his business affairs or his work. For her fate in life is bound up together with him and they share a common lot, and thus true peace in the home is established. (Rabbi Ben-Tziyyon Meir Ĥai Uziel, Hegyonei Uziel)

Of all types of holiness, none compares to the holiness of marital intimacy, if it is performed with holiness, and he sanctifies himself. (Shelah, Sha’ar Ha’otiot, Kedushat Hazivug)

Further reading: For the story of the daughters of Tzelofhad, see A Concise Guide to the Torah, p. 409.