Four entered the Orchard (Pardes). They were Ben 'Azzai, Ben Zoma, Aher (the Other) and Akiba.

Rabbi Akiba warned, "When you enter near the stones of pure marble, do not say 'water water,' since it is written, 'He who speaks falsehood will not be established before My eyes'" (Psalms 101:7).

Ben Azzai gazed and died. Regarding it is written, 'Precious in God's eyes is the death of His saints' (Psalms 116:15).

Ben Zoma gazed and was stricken. He went insane. Regarding him it is written, 'You have found honey, eat moderately least you bloat yourself and vomit it' (Proverbs 25:16).

The Other gazed and cut his roots (became a heretic). Where there is One, he saw two, and thus emerged an apostate.

Rabbi Akiba entered in peace and exited in peace...

The angels also wished to cast down Rabbi Akiba but the Blessed Holy One said, "Leave this elder alone, for he is worthy of making use of My glory."

This teaching works through a pun. “PaRDeS,, composed of the four consonants, PRDS (פרדס), is an acronym for the four rules of Biblical exegesis:

Peshat (simple understanding):

• "Peshat" = "simple;" the plain meaning of the text in its immediate context, understanding each word in terms of its common usage. According to Shabbat 63a, a verse never loses its simple meaning.

Remez (allusion), a poetical level:

• "Remez" = "hint;" generalizing the meaning of a verse, so that it functions metaphorically or allegorically.

Drash (inference) an interpretative level:

• "Drash" = "conceptual;" a more detailed exposition or interpretation of the peshat or remez (often by juxtaposing different verses to elicit new meanings), often to make a moral point.

and Sod (secrets) where we plumb the mystical depths.

• "Sod" = "hidden;" an esoteric or mystical reading of the text.

This teaching could be read to mean that these four sages together sought to achieve an absolute, perfect understanding of the Torah in all its complexity, on all its levels. Kabbalists see these four methods as stages through which a mystic can use Biblical interpretation to fathom the depths of reality until one has a direct encounter with the divine truth.

The four rabbis who entered Pardes were, in fact, trying to rectify the sin of the first man, Adam HaRishon, a monumental task that, apparently, they were not as capable of doing as they had hoped they would be. They were trying to enter the level of consciousness that Man enjoyed prior to his sin in order to rectify it, because there is a concept that one can only atone for a sin if he can return to the level upon which the sin was committed.

They had mastered Mikrah - the simplest explanation of the entire Torah - and they knew the entire Mishnah on the level of the Talmud. They had mastered Pshat, Remez, and Drush. And, as is evident from the story, they had sufficiently mastered Sod - Kabbalah - to enter Pardes, but not enough to withstand the profound tests of reaching such sublime levels of consciousness: Ben Zoma went insane, Ben Azzai died, and Elisha ben Abuya became a heretic. Even Rebi Akiva needed special Divine protection to withstand the wrath of the angels.

Some would like to learn from this a reason to stay away from Kabbalah. However, the true lesson is that Pardes is attainable, but one must not go beyond the level suitable for him.

Think of Pardes as ladder between the world we live in and G-d Himself. Pshat is the first rung on the ladder, Yetzirah is the second rung, Beriyah is the third, and Atzilut is the fourth. Should we not climb it? To remain on the ground, that is, on the level of Pshat is to remain in the world of physicality, and be vulnerable to the enemies of truth.

Let me give my own brief Midrash (commentary) on it:

• The Orchard (Pardes, from which we get the word Paradise), is a different dimension of reality, not accessible by usual means of sight, touch, hearing. It can be accessed by use of the methods of Kabbalah.
• Ben Azzai gazed and died. He was not ready to handle what he saw.
• Ben Zoma gazed and got sick - of some sort. The text helps us by implying that he took on more that he could 'swallow.'
• The Other - the Talmud does not say who that was, but it is widely known to be Elisha ben Abuya, so Kaplan inserted that name in his translation - gazed and cut the plants, which is interpreted as becoming a heretic. Because it is interpreted as him cutting of the roots that fed him.
• R. Akiba entered in peace and left in peace, but through no doing of his own. The text explicitly says that only the intervention of the Blessed Holy One is the the reason he was able to return. So a bit of mazal helps :)