Resurrection of the Dead (Techi’at Hameitim)
In order to fully grasp the concept of the resurrection of the dead, one must first understand the true purpose of death. In the beginning, when G-d created Man, He intended for him to live eternally. However, when Adam sinned, death was decreed upon Mankind as a result.
At first glance, death seems like a very harsh punishment for only one sin. It also doesn’t seem fair for all humans to have to pay for a sin they themselves did not commit.
According to esoteric teachings Adam, being the first man, included within him all of the potential souls which were to be born, so when he sinned in the Garden of Eden, the future of all humanity was directly affected.
Thus, the Arizal explains based on Kabbalah: “Know, according to esoteric teachings, the entire nation of Israel is like one body which was included in the soul of Adam harishon… and each person is like a particular limb of a body, and this is what is meant that all Jewish people are connected one to another if they sin… when one person sins it is as if the other also sins, therefore the text of confession was established in the plural form.” (When a person does a mitzvah as well, it can help another person.)
As a result of the first sin all of Mankind became blemished together with Adam; all must take part in repairing the damage. If Mankind was to live forever in this new state, Man would remain imperfect forever. So, G-d, in His infinite wisdom, decreed that Man must die, for only through death and decay could the body and soul acquire their full tikun (repair) and eventually regain the perfection (shleimut) that was once theirs.
After the sin, the body became much more attached to evil, and the soul's job of refining and elevating the physical body became so difficult that one lifetime would no longer be enough. The world at large was also affected by Man's sin and must also be fixed. This is the deeper meaning of what the Sages say, that the world will be for six thousand years, then for one thousand years the world will be desolate, and then G-d will rebuild the world anew. At that time G-d will resurrect the dead, reuniting body and soul. In this new state the soul will be able to purify the body completely, resulting in their total unification. Body and soul will then both partake of the eternal life of reward which was intended from the beginning (See Derech Hashem, ch. 1, part 3, authored by the Ramchal, Rabbi Moshe Chaim Lutzatto 1707–1746).