The Zohar says that even though Moses was the teacher of all Israel, his interpreter was Aaron the Kohen. (Rayah Mehemna, Bereishit 25b; 253) As it says, "He will be a mouth for you" (Ex. 4:16) since Moses had a "heavy mouth" and a "heavy tongue". (Ex. 4:10)

"The brit [covenant] of the flesh and the brit of the tongue." The concept of brit is the medium of relation to another. The source of course is God creating a world and choosing to relate to it. The point of the giving of the Torah is to show this relationship. Moses is the channel of the giving of the Torah. He was so healed by the giving of the Torah from his lisp.

The tikun of the giving of the Torah was disrupted by the sin of the golden calf. (Ex. 32:7) In this sense the relationship of God to His world was impaired, and Moses the channel automatically suffered.1

The final redemption will not only restore the level of the giving of the Torah, it will also further enhance it.

Even in the imperfect state of Moses’s lack of oratory the Divine message can come and relate through the concept of an interpreter. He stands a rung down and delivers the light to the people in a way they can accept.

This is also one of the ways that Elijah dispels falsehood - by his eloquent ability to bring the light down and feed it to those on low levels.

In the end of days in the generation of Mashiach, Moses will return to teach Torah to Israel and will still be of "uncircumcised lips".2 However, Elijah, who will chai [live] will be his interpreter, and this is the secret of the verse, "Pinchas (who became Eliyahu) the son of Elazar the son of Aaron the Kohen". (Num. 25:11) This is as it is written, "If [one is drawn] to laitzim [scoffers], he will scoff". (Prov. 4:37) ("Laitzim" derives from the same root as the word ‘mailitz’, meaning an orator/spokesman) When they will need a translator for Moses, Elijah who will live will translate and be Moses’ spokesman.

Thus Elijah, who is Pinchas, who is a kohen, takes the place of his grandfather. Aaron the Kohen.

In the order of the seven grand shepherds of Israel, Aaron identifies with hod. (Ari.Zl.) Hod is the source of the power of speech, which is revealed in malchut/the mouth. (Tikunei Zohar, Intro.) It is actually the last sefira - malchut and yesod being but inclusive of what is above them. (Tikunei Zohar, Intro.) It means splendor. Its job is to constrict and transmit the supernal splendor to the below. Through this above and below unite and all bounty flows and is revealed. (Zohar)

Eliyahu/Elijah equals 52 - twice the Tetragrammaton. This hints to his special power to bring Divinity on high together with what is beneath it.

[Translation and commentary by Perets Auerbach.]