Bodies of Yemos Hamoshiach

Maamarim Admor Ha'emtzo'i

It is known that Techiyas Hameisim comes after the days of Moshiach. Even though in the days of Moshiach the bodies will be completely cleansed from their materiality because then the Eitz Ha'Da'as Tov v'Ra will be completely refined and "I will remove the spirit of tuma from the earth." Even animals and beasts..."and everyone will know Me" and the earth will be filled with the knowledge of Hashem mamash. Nonetheless, they will be in physical bodies that were born from a mother and father amidst physical desire, except they will not possess any evil at all. Their avodah in Torah and Mitzvos will be b'pnimiyus davka, as in the expression "hilchasa d'Meshicha" [the halachos for the days of Moshiach, Sanhedrin 51b, Zohar I:114].

Thus we say "there we will perform mitzvos before you as mitzvos ratzonecha (commandments which you have willed)"... as the sages say, there is no difference between this world and the days of Moshiach except for enslavement to the nations. Only that the avodah will be via the ruchniyus, and not like Adam Harishon in Gan Eden to work it (b'ruchniyus mamash) but rather within gashmiyius davka, as it says "And strangers shall stand and pasture your sheep, and foreigners shall be your plowmen and your vinedressers" (Yeshaya 61:5).

The lifespan will be lengthened ("a youth of one hundred will die") but they will die nonetheless because the body will not yet be sufficiently refined to be like Adam Harishon before the sin, when there was no death at all. But at Techiyas Hameisim all the neshomas who passed away will come up and up to their bodies with the supernal dew that will revive them, and flesh and sinew and bone will cover them and they will live via supernal life...these will be holy bodies, completely pure, not created from the desire of a physical union of father andmother, and thus there will be no death for them like Adam Harishon before the sin--that his body was holy, comparable to his neshoma (to the degree that his heel was as bright as the sun, his heel being in Asiyah but still totally separated from any mixture of good and evil) and soul and body were like form and substance and so too his sons born before the sin.

Vayikra B, L'ag B'Omer, p.685-6 (part 15)

[Important to note that the 7th Lubavitcher Rebbe has stated that because golus has extended so long, r"l, our generation will be able to transition from our present physical being to eternal life without the need for death in the interim (ללא הפםק בינתים).]