Any space mission involves two major challenges: One is launching the shuttle into outer space with sufficient energy to overcome the pull of earth's gravity. The second challenge is returning the spacecraft to earth, without it getting burned by the extreme temperatures in earth's atmosphere, or getting crushed on impact.
The Talmud (Chagiga 14:2) describes a similar, spiritual "launch" undertaken by four well-known sages: Ben Azai, Ben Zoma, Elisha Ben Avuya, and Rabbi Akiba. All four of them entered Paradise. The word “Paradise” is an acronym for four levels of Torah's interpretation: Pshat (the simple interpretation), Remez (allegorical), Derush (homiletical) and Sod (mystical.)
The takeoff passed peacefully, and the four penetrated the deepest levels of Torah. However, only one of the four, Rabbi Akiba, merited to return in peace and bestow upon mankind the spiritual treasures that he acquired. The other three were adversely affected by their experience and did not make it back intact.
Chassidic philosophy explains the inner meaning of this tale. When one embarks on the study of the deepest interpretations of Torah, he leaves behind his corporeal awareness of the universe and experiences a completely spiritual state of consciousness. However, it's possible to become so enamored by this spiritual reality that one forgets the physical world awaiting him back home.
In order not to become lost in this spiritual state, there must be a defined purpose from the outset. The launch must be with the intention of returning from “up there” laden with energy to use in the service of the creator. The heightened awareness of spirituality must be integrated within the confines of the body, in the time and space of our world, the lowest and most physical of all possible realities.
This is why, in the wording of the Talmud's story, only of Rabbi Akiba does it say that he "entered in peace." Only he initially entered the spiritual realm with the intention of making peace - of bridging the gap between physical and spiritual. He entered Paradise not to disconnect himself from the physical world, but rather to derive energy to make the physical world into a home for G-d. Since his "takeoff" was peaceful, his landing was peaceful as well.
The student and successor of Rabbi Akiba, Rabbi Shimon Bar Yochai, whose passing we commemorate on Lag B'omer, followed in his footsteps. He taught the Torah's most innermost dimensions and bequeathed them to subsequent generations, through his authorship of the Zohar. These teachings are a foretaste of the Torah that Moshiach will reveal, and through its study we will merit to "go out of exile in peace."