(Exodus 4:15) If it is said, "I will be with your mouth," why is it said, "and I will instruct you"? And if it is said, "and I will instruct you," why is it said, "I will be with your mouth"? Rather, "I will be with your mouth" refers to the opening of the mouth and the answer of the tongue. "And I will instruct you" refers to the treasuries of wisdom that the Holy One, blessed be He, revealed to Moses concerning all the treasuries of Torah, wisdom, and knowledge, and the treasuries of life; and He showed him what is destined to be in the World to Come. And when he saw, behind the curtain of the Holy One, blessed be He, company upon company of the Sanhedrin who would sit in the Chamber of Hewn Stone and expound the Torah in forty-nine aspects, and He showed him Rabbi Akiva expounding the crowns of the letters, he said, "I have no business in the mission of the Omnipresent," as it is said, "And he said, please, my Lord, send by the hand of whomever You will send" (Exodus 4:13). What did the Holy One, blessed be He, do? He dispatched the Prince of Wisdom, who seized Moses and led him to a certain place, and showed him, behind the curtain of the Holy One, blessed be He, myriads upon myriads of the Sanhedrin sitting and expounding and declaring, "It is a law given to Moses at Sinai." Immediately Moses' mind was set at ease.
What the LORD Showed Moses Before Sending Him
Yalkut Shimoni on Torah 173:2
(שמות ד טו) אִם נֶאֱמַר אֶהְיֶה עִם פִּיךָ לָמָּה נֶאֱמַר הוֹרֵיתִיךָ, וְאִם נֶאֱמַר הוֹרֵיתִיךָ לָמָּה נֶאֱמַר אֶהְיֶה עִם פִּיךָ, אֶלָּא אֶהְיֶה עִם פִּיךָ זֶה פְּתִיחַת פֶּה וּמַעֲנֵה לָשׁוֹן. הוֹרֵיתִיךָ, זֶה גִּנְזֵי חָכְמָה שֶׁגִּלָּה הַקָּדוֹשׁ בָּרוּךְ הוּא לְמֹשֶׁה עַל כָּל גִּנְזֵי תּוֹרָה חָכְמָה וּמַדָּע וְגִנְזֵי חַיִּים, וְהֶרְאָהוּ מַה שֶּׁעָתִיד לִהְיוֹת לְעוֹלָם הַבָּא. וְכֵיוָן שֶׁרָאָה בַּפַּרְגּוֹד שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא כִּתּוֹת כִּתּוֹת שֶׁל סַנְהֶדְרִין שֶׁהָיוּ יוֹשְׁבִין בְּלִשְׁכַּת הַגָּזִית וְדוֹרְשִׁים הַתּוֹרָה בְּמ"ט פָּנִים, וְהֶרְאָהוּ רַבִּי עֲקִיבָא דּוֹרֵשׁ כִּתְרֵי אוֹתִיּוֹת, אָמַר אֵין לִי עֵסֶק בִּשְׁלִיחוּת שֶׁל מָקוֹם, שֶׁנֶּאֱמַר וַיֹּאמֶר בִּי אֲדֹנִי שְׁלַח נָא בְּיַד תִּשְׁלָח, מֶה עָשָׂה הַקָּדוֹשׁ בָּרוּךְ הוּא, שִׁגְּרוֹ לְשַׂר שֶׁל חָכְמָה וּתְפָשׂוֹ לְמֹשֶׁה וְהוֹלִיכוֹ לְמָקוֹם אֶחָד וְהֶרְאָה לוֹ בַּפַּרְגּוֹד שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא רִבּוֹא רְבָבוֹת שֶׁל סַנְהֶדְרִין שֶׁיּוֹשְׁבִים וְדוֹרְשִׁים וְאוֹמְרִים הֲלָכָה לְמֹשֶׁה מִסִּינַי, מִיָּד נִתְקָרְרָה דַּעְתּוֹ שֶׁל מֹשֶׁה.