Resurrection

The leap from Yemos HaMoshiach to the period of Techiyas HaMeisim (Resurrection of the Dead) is far greater than the leap from our period of history to Yemos HaMoshiach. For, whereas in Yemos HaMoshiach new bodies will be brought into the world through the familiar birth process, in Techiyas HaMeisim they will be built anew just like Adam HaRishon's body was at the beginning of Parashas Bereishis:

... It is like a craftsman who extracts silver from its source in the ground; in the beginning he puts it into an oven until all the impurities of the ground are removed, and the silver remains. But not perfect silver, until he puts it into the over again Likewise, The Holy One, Blessed is He, puts the body into the ground until it completely rots and all of the zuhama is removed, and only a small amount of decomposed matter remains. From this He re-builds the body... (Zohar, Vayaira 115b-116a)

At the beginning, He will build the body from the small amount of decomposed matter, which will be clean and pure from zuhama. However, it will still be quite physical and not in its true perfected state. (Sha'arei Leshem, p. 490)
The purpose of resurrection is clear: it is to rebuild the body free of any impurities, so that it can return to its ideal state of 'Kesones Ohr' (aleph-vav-raish), when it is more soul-like than body-like. How long this process takes is the same for every person, however, just when the process begins will vary from person to person:

The time of resurrection will vary, for, one who is rectified earlier from his zuhama will die and resurrect earlier, since the point of death then will only be to decay the physicality of the body and renew it as a new entity. As a result, the period of death to resurrection for the entire 'generation' will be long, though, tzaddikim who have died previously will resurrect immediately at the beginning of the period, which will be after forty years of the ingathering of the exiles (Sha'arei Leshem, p. 489)

This is what it says in Midrash:

There will be many resurrections, and the period of time will continue, according to Rebi Yehudah from forty years after Kibbutz Golios, at which time the first resurrection will occur, and continue until the last resurrection, a period of 210 (year 2030) years. Rebi Yitzchak says: 214 years (tear 2026). (Midrash Ne'elam, Toldos 140a)

Explains the Leshem: there will be many resurrections over a large period of time, with the first resurrection occurring after forty years of ingathering of exiles, that is, 210 years in advance of Year 6000. The last resurrection will occur towards the end of the 210 years:

They will not all die at the same time, for, the world will not be destroyed in advance of Techiyas HaMeisim. Rather, some will die early, and some later, just as it is now. It will continue this way for a long time-the entire forty-year period of Kibbutz Golios until the first resurrection, as well as the entire 210 years or 214 years after the first resurrection until the last resurrection, as we mentioned previously. Anyone who is not yet rectified by the time resurrection begins as is fitting for eternal life, will die at the end. (Sha'arei Leshem, 490)
Hence, during the period of 210 years, some people will have already resurrected, whereas others will still await death, decomposition, and, resurrection. However, whereas on this side of history we fear death and long to live, on THAT side of history we will long to finally die and be recreated anew:

All those who still live the life of This World will say 'Holy!' before the righteous who have already arisen during the resurrection. The world will exist on two levels: that of angels and that of man. (Sha'arei Leshem, p. 490)

In such a spiritually holy environment, it will be impossible to ignore one's own physicality, and, the sooner one dies, the sooner one will be able to join the ranks of the angels.
Many questions arise as a result of the concept of resurrection, since it represents the 'final form' of the person (though it can become increasingly spiritual as time progresses and creation becomes more elevated). However, when we consider the concept of 'gilgulim, that is, reincarnation, then the question arises, which body returns in Techiyas HaMeisim?
After all, reincarnation implies that a single soul can live many lives. And, furthermore, in the course of living many lives, he may have had many wives, and she, many husbands-one per lifetime. For whom do we resurrect?
The answer is not so simple, and, it is beyond the scope of this discussion to fully provide it, even if that were possible. However, some details are available, beginning with:
Look also in the Zohar (Chaye Sarah 126a), where it says that the resurrection will literally occur ... in the body that suffered with the soul in This World and did not derive any pleasure from the entire Torah and his good deeds ... after it is purified from all its zuhama and physicality, as a result of death and decomposition in the ground, as it is explained. (Sha'arei Leshem, p. 489)

Thus, according to the Leshem, the body that was used the most to learn Torah and to perform mitzvos, with the least amount of worldly benefit for doing so, is the one destined to be resurrected. Considering that Torah and mitzvos themselves are meant to act as a process of refinement, that would make sense.

And, the less worldly benefit derived for learning Torah and doing mitzvos would mean that the person did both for altruistic reasons, adding to the purification process of the body. For, nothing purifies the body more than serving G-d for HIS sake, and not for our own sake; it is considered as if the person sacrificed himself on the altar as a sacrifice to G-d and ascended Heavenward.

However, as we will see from the Arizal, it is not so simple which body returns in Techiyas HaMeisim, or, for that matter, how many.