This article is an excerpt from our Sefer
14. The intimacy of souls and the union of husband and wife in Gan Eden:
The union of matrimony is not only practiced in this world, but is also practiced in the next world, in Gan Eden. Thus, even in Gan Eden the souls of a husband and wife engage in intimacy. Those couples who were married in this world continue their relationship in Gan Eden, as souls. Just as their union in this world brought about physical children, so too, in Gan Eden their union brings about spiritual children. These passionate unions of the souls of the husband and wife create souls that are eventually born in this world. The time of marital union [i.e. Zivug] of these souls is every midnight. Thus, Avraham and Sarah until this day engage in marital intimacy in heaven during midnight and have souls born to them as a result. These souls eventually descend into the bodies of converts and bring them towards a Halachic conversion, making them into Jews. What causes that a gentile suddenly gets aroused with a passion to convert is the fact that he has now received this soul that was created by Avraham and Sarah through their intimacy in Gan Eden during midnight. Now, just like in this world you have couples who cannot have children, so too in the next world there are souls who are barren and cannot produce souls.
How intimacy takes place without a body: Obviously, this intimacy is not one of physical bonding, as there are no bodies in heaven, but rather an attachment of the souls. The same way there physically exists the abilities to hug, kiss, bond and ejaculate, so too spiritually, these aspects likewise exist, and couples can engage in them in heaven. It is the soul itself which has the power to procreate, and this power is not only limited to when it is within a physical body. Just like in the physical body the soul pumps into the semen an extension of itself that allows a new soul to be created, so too in the spiritual intimacy that takes place in heaven, the soul extends itself during intimacy to duplicate another soul. The same way in this world the father provides the physical seed to the mother who absorbs it and develops it, so too spiritually in heaven, the father provides the spiritual seed to the soul of his wife who receives it and develops it. The spiritual seed of the husband remains inside the soul of the wife for nine months of gestation, just like it is in this world, and after nine months the soul is born and can enter into a body.
 See Ma’amarei Admur Hazakein p. 151 “Lehavin Inyan Zivug Haneshamos”; Derech Mitzvosecha Peru Urevu p. 3a; Sefer Hachakira p. 56a; Eitz Chaim Sha’ar Tikkun Nukvah 34:1; 39:11; Eitz Hada’as Tov Parshas Ki Savo p. 27; Ta’amei Hamitzvos p. 5; Zohar Bereishis p. 21; Lech L’cha; Rav Poalim 2 Sod Yesharim 2
 See Ma’amarei Admur Hazakein at length