"zeh lecha ha'os" -- the sign Moshe was given

Moshe was reluctant to assume the mantle of leadership.  He said to G-d:

 וַיֹּ֤אמֶר מֹשֶׁה֙ אֶל־הָ֣אֱלֹקים מִ֣י אָנֹ֔כִי כִּ֥י אֵלֵ֖ךְ אֶל־פַּרְעֹ֑ה וְכִ֥י אוֹצִ֛יא אֶת־בְּנֵ֥י יִשְׂרָאֵ֖ל מִמִּצְרָֽיִם

The Midrash comments:

רִבּוֹן הָעוֹלָמִים, כְּשֶׁיָּרַד יַעֲקֹב לְמִצְרַיִם לֹא כָּךְ אָמַרְתָּ לוֹ:: אָנֹכִי אֵרֵד עִמְּךָ מִצְרַיְמָה וְאָנֹכִי אַעַלְךָ גַּם עָלֹה (בראשית מ״ו:ד׳), וְעַכְשָׁיו אַתָּה אוֹמֵר לִי: לְכָה וְאֶשְׁלָחֲךָ אֶל פַּרְעֹה, לֹא אָנֹכִי הוּא שֶׁאָמַרְתָּ לוֹ: וְאָנֹכִי אַעַלְךָ גַּם עָלֹה

Moshe said to G-d, "You promised that you would be with the people in their exile and that you would redeem them.  I am not you!  It is not my place to take on this task."

To which G-d answered,  כִּֽי־אֶֽהְיֶ֣ה עִמָּ֔ךְ.  I, אָנֹ֔כִי, am the redeemer, but I will act through you.  

The pasuk (3:21) then continues that Hashem gave Moshe a sign:

 וְזֶה־לְּךָ֣ הָא֔וֹת כִּ֥י אָנֹכִ֖י שְׁלַחְתִּ֑יךָ בְּהוֹצִֽיאֲךָ֤ אֶת־הָעָם֙ מִמִּצְרַ֔יִם תַּֽעַבְדוּן֙ אֶת־הָ֣אֱלֹקים עַ֖ל הָהָ֥ר הַזֶּֽה׃

How does this sign help Moshe prove his bona fides or prove that G-d is with him?  The fact that mattan Torah will take place 50 days after yetzias Mitzrayim will not help Moshe up front, before yetzi'as Mitzrayim takes place, when he has to convince the people to follow him?!

Meshech Chochma and Ohr haChaim say an amazing pshat here.  You have to put the period in the right place in the pasuk.  וְזֶה־לְּךָ֣ הָא֔וֹת כִּ֥י אָנֹכִ֖י שְׁלַחְתִּ֑יךָ -- period, full stop.  This is the sign!  What is the "this" they are talking about?  It's the previous sentence.  There are a lot of people who, if offered the chance to become the leader of a nation, would jump at the chance.  There are people who would demur, but out of a false sense of humility.  That works when you are speaking to a human being, but it does not work when you are speaking to G-d, as He is able to tell exactly what is in your heart and can tell whether you really want the job or not.  False modesty does not work.  It's only a Moshe Rabeinu who can say b'lev shalem, with sincerity and in absolute truth, מִ֣י אָנֹ֔כִי כִּ֥י אֵלֵ֖ךְ אֶל־פַּרְעֹ֑ה, I really don't think I am worthy of the job. Hashem told Moshe, "That is the only sign you need."  People can detect true humility and sense sincerity.  They will recognize that only someone of your caliber, only someone who would turn down the job, could possibly be the one chosen by Hashem.

The proof that humility is the quality that defines who the go'el is בְּהוֹצִֽיאֲךָ֤ אֶת־הָעָם֙ מִמִּצְרַ֔יִם תַּֽעַבְדוּן֙ אֶת־הָ֣אֱלֹקים עַ֖ל הָהָ֥ר הַזֶּֽה. The same זֶה, the same humility, that characterized Moshe's response, is the same זֶה -- the mountain of הָהָ֥ר הַזֶּֽה--  that made Har Sinai into the mountain where mattan Torah would take place.  As Chazal tell us, it's not because Har Sinai was the tallest or greatest mountain that it was chosen; it's because it was the lowest mountain, symbolizing the humility necessary to be a conduit of dvar Hashem.