1. The purpose of intimacy – Why G-d commanded us to engage in intimacy and why He created this method of procreation:[1]

There are two reasons for why G-d commanded us to engage in intimacy.

1. Peru Urevu: The main reason for intimacy is simply for the sake of having children.[2] This is the second intent mentioned by the Poskim[3] regarding why one should engage in intimacy. Many in fact even write that this is the only purpose of intercourse.[4] This is evident from the fact that as soon as one ejaculates his desire expires and he no longer lusts for it.[5] This is also evident from the fact that the reason why we do not say a blessing of Mitzvos on Kiddushin is due to that the purpose of marriage is procreation.[6] Likewise, due to this reason we do not say a blessing prior to intercourse.[7] Likewise, due to this reason, according to Talmudic law, if one is married for ten years without children, then he must get divorced and remarry.[8] On this Rebbe Yossi would say that one should not call his wife, “his wife,” but rather, “his house,” as the purpose of the wife is for bearing children.[9] This follows the Talmudic Sage who would say that the purpose of a wife is only for bearing children.[10]
2. Onah – Loving thy wife – Unity of the body and soul:[11] Another reason that G-d created intimacy is in order so the couple love each other and unite to become one body and one soul, independent of the birth of physical children. This is known as the Mitzvah of Onah which is the main discussion in the Poskim[12] for why one should engage in intimacy. The independency of the Mitzvah of Onah from the Mitzvah to have children can be proven from the fact that the Mitzvah of Onah applies even when the wife cannot become pregnant.[13] The purpose of the Mitzvah of Onah is to provide one’s wife with the physical love that she yearns for, and hence one does not fulfill his Mitzvah of Onah if he does so for his own pleasure and does not rejoice his wife.[14] In Kabbalah, this Mitzvah is more deeply explained by elucidating that its purpose is not just to show the wife love but to truly desire to unite with one’s wife with a passion of holy fire.[15] This independency of intimacy from procreation can also be proven from the fact that the Torah commands us to rejoice the wife in the first year, and during the Holidays.[16] This can also explain why today the custom is to remain married to one’s wife even after ten years have passed without children.[17] This also explains why the Shechina dwells in the intimacy of a couple, even prior to the birth of children, and even when pregnancy is irrelevant.[18] On this, other Tana’im would say that there were days when they would call their wives, “my wife,” as the purpose of the wife is not just for bearing children, but also to unite together with her husband.[19] This follows the Talmudic Sage who would say that the purpose of a wife is only for beauty.[20]

The above two reasons are really one: In truth, the second reason is an explanation of the first, as why is it that G-d arranged that intimacy be a prerequisite for children? The reason for this is because he desired that man be created by unity of the husband and wife. In fact, all the spiritual worlds evolve through the unity of the masculine and feminine Sefiros. Thus, just as all the spiritual worlds unite around love and unity, so too the physical world likewise lives off love and unity. Accordingly, it is understood that intimacy is something intrinsically holy which corresponds to the unity of the worlds, and it is due to its great holiness that it has the ability to cause procreation. Thus, the husband and wife unifying with each other during intimacy is a goal in its own right, which then brings fruit to fulfilling the second goal of having children. Furthermore, as explained in Sifrei Kabbalah,[21] souls are born in heaven from every union of a husband and wife, and thus the love and bonding of the couple is synonymous with procreation, either physical or spiritual, and they are not two separate things, as every procreation requires love and intimacy, and every love and intimacy effects at least spiritual procreation of souls.

[1] See Likkutei Sichos 17:174

[2] Rambam Issureiy Biyah 21:9

[3] Michaber O.C. 240:1; 231; E.H. 25:2; Tur 240 in name of Ra’avad that this is the greatest of the intents; Rambam Pirush Hamishnayos Sanhedrin 7:4; Mikdash Melech on Zohar Vayikra 43a; Siddur Kol Yaakov Arizal p. 112; Sefer Habris 1:17-2

[4] Rambam Pirush Hamishnayos Sanhedrin 7:4; Ramban Vayikra 18:6; Sefer Ikkarim 1:8; Rabbeinu Bechayeh Devarim 23:2; Likkutei Sichos 17:174

[5] Rambam Pirush Hamishnayos Sanhedrin 7:4

[6] See Rosh Kesubos 1:12

[7] Halachos Ketanos 1:137 based on Rashba

[8] Michaber and Rama E.H. 154:10; Rama E.H. 1:3; Mishneh and Gemara Yevamos 64a

[9] Shabbos 118b “Rebbe Yossi said: In all my days I did not call my wife my wife, but rather called her my house.”

[10] Kesubos 59b

[11] See Reishis Chochma Sha’ar Hakedusha 16:2; Zohar Kedoshim p. 81a; Siddur Yaavetz Mosach Hashabbos Mitos Kesef 7 Chulya Beis 13; Implication of verse “Al Kein Yazov Ish Es Avivi Vies Imo Vidavak Beishto Vehyau Lebasa Echad”; See Ramban Bereishis 2:24 that this is the difference between the mating of animals and that of humans, that by animals, it’s a mere act of procreation, and there is no D’veikus between the male and female. However, by humans, we attach to our wives; See also Ra’avad in Ba’alei Hanefesh in Hakdama for a similar explanation. However, see Sheyikadesh Atzmo Shut 8 which claims that the above does not refer to the feelings of love during intercourse, but simply in general to the love a husband has for his wife and vice versa

[12] Michaber 240:1; 231; Tur 240:1; Ra’avad in Ba’al Nefesh Sha’ar Hakedusha; Reishis Chochma 16:24; Mikdash Melech on Zohar Vayikra 43a; Siddur Arizal of Rav Shabsi; Taharas Yisrael 240:19

[13] See Chapter 2 Halacha 2E!

[14] See Chapter 2 Halacha 1 in Q&A!

[15] Reishis Chochmah Sha’ar Hakedusha 16

[16] Likkutei Sichos ibid

[17] Rama 1:3; 154:10; Rivash 15; Hagahos Maimanis Ishus 15:4 in name of Ravayah [Aviasaf] “We no longer force to divorce even in Israel as the Talmud states that after the destruction it would have been proper to decree not to have children and hence at the very least we do not force a divorce upon such a couple.”  

[18] See Likkutei Sichos ibid

[19] See Likkutei Sichos ibid

[20] Kesubos 59b

[21] See Halacha 13