Our Gemara on Amud Aleph mentions our tradition that the prophet Elijah never really died. The verses allude to this as well. In Malachim

II:2:11 it states: “and Elijah went up to heaven in a whirlwind.” While that doesn’t explicitly tells us that he will remain on this earth, Malachi (3:23) prophesies that Elijah will return to us in the times of the Mashiach: “⁦Lo, I will send the prophet Elijah to you before the coming of the awesome, fearful day of the LORD.” But regardless of the verses, we have a tradition that he indeed is really alive.

The way it comes up in our Gemara is that a proof is brought that one tears his clothes upon the death of his Rebbi, and a tear that is not ever mended, from Elisha’s behavior after Eliyahu “died”. Which of course brought a question from the Gemara, but indeed, Eliyahu did not die! And to this, the Gemara answers that since Elisha knew he would never see Eliyahu again, it was if he was dead to him and warranted the same mourning rituals.

If so, perhaps it is justified to do keriya (ritual tearing of garments) if you are taking leave of your Rebbi and know you will never see him? Meiri says we do not say that despite what transpired between Elisha and Eliyahu and then cryptically says, סוד ה׳ ליראיו the secrets of Hashem belong to those who fear Him. A rabbinic catchphrase used when there is some kind of mystical or theological secret that cannot be stated explicitly but must be read between the lines. So what’s the Meiri hinting at?

The subject matter is Eliyahu and if he is alive or not. Since Meiri ruled that Elisha’s absence of a rebbe which induced mourning rites is not literally compared to another student who will never see his rebbe again, I think we can surmise the subject matter of this secret lore has to do with Eliyahu’s status of being alive and not dead.

Indeed there is a halakhic Shaalah discussed in Beis Shmuel Shulkhan Arukh (EH:17:11) and Terumas Hadeshen II:102 would Eliyahu Hanavi’s be permitted to marry another man. They did not consider this a foolish question, as they believed if Eliyahu could reach this level

Of spiritual attainment, so might someone else in the future. The ruling is that his wife may remarry as Eliyahu metamorphosed into an angel-like being and was no longer human. So we see that Meiri’s hesitation to consider Eliyahu alive in a human sense is warranted also from analysis of the poskim.

In trying to understand Eliyahu’s metamorphosis, we might presume that his spiritual attainment was so high that he transcended the restrictions of physicality. However, does this not create a theological problem. How could his spiritual attainment exceed that of Moshe, who was the greatest of all prophets and spoke face to face with God (as described in the beginnings of Bamidbar 12). 

Believe it or not, Rabbbenu Bechaye (Devarim 34:5) says quite simply, due to Moshe’s sin by the waters of strife he was doomed to die (Numbers 20:12).

Abravanel (Melachim II:2:18) offers a different explanation. He says indeed, because Moshe reached the highest spiritual state, his body was made completely irrelevant and he graduated fully with his Soul. Yet Eliyahu, though he reached a high level to the extent that much of his body was converted into spiritual material, it still remained in some way Physical. Therefore, he retains his body. An additional reason is that Moshe and Eliyahu had different functions. Moshe’s function was to be the human being that transcended all and became fully attached to God. In that sense, there is nothing for him to do more in his lifetime other than to migrate to heaven. On the other hand, Eliyahu‘s mission was to constantly be involved with people. This is why he continues to appear to great stages and teach them Torah, and also will one day be the harbinger of the Messiah.