It is known that the Resurection of the Dead will be after the days of Moshiach[...] Now, in the days of Moshiach the bodies will be completely refined, as it says "I will remove the spirit of impurity from the land," and as a consequence of the removal of the impurity, all the materiality and physicality will be refined, until even among animals and beasts the pollution will cease. This is as it states "the wolf will dwell with the lamb and the cow and bear, etc"
Specifically it the bodies of human beings that will be the most refined, but nonetheless there will be bodies which will be born from a physical mother and father from a natural physical desire. This desire, however, will not be a material desire at all, and there will be no admixture of evil in it, as it says in the Zohar "the tree of knowledge of good and evil will be removed from the world" (Zohar III 124b). Nevertheless, there will be a natural desire, and this is like Adam Harishon before the sin, that he didn't have material desires at all, just the "will", like the "will" to eat, not for fulfilling his desires but rather for the connection of the soul and body that comes about from the eating. And so, too, the union of man and woman was out of the desire to bring children.
Sefer Hamaamorim 5711 (Rebbe Rayatz) p.20