וַיֹּאמֶר מֹשֶׁה אֶל-הָאֱלֹהִים, הִנֵּה אָנֹכִי בָא אֶל-בְּנֵי יִשְׂרָאֵל, וְאָמַרְתִּי לָהֶם, אֱלֹהֵי אֲבוֹתֵיכֶם שְׁלָחַנִי אֲלֵיכֶם; וְאָמְרוּ-לִי מַה-שְּׁמוֹ, מָה אֹמַר אֲלֵהֶם. וַיֹּאמֶר אֱלֹהִים אֶל-מֹשֶׁה, אֶהְיֶה אֲשֶׁר אֶהְיֶה; וַיֹּאמֶר, כֹּה תֹאמַר לִבְנֵי יִשְׂרָאֵל, אֶהְיֶה, שְׁלָחַנִי אֲלֵיכֶם. וַיֹּאמֶר עוֹד אֱלֹהִים אֶל-מֹשֶׁה, כֹּה-תֹאמַר אֶל-בְּנֵי יִשְׂרָאֵל, יְהוָה אֱלֹהֵי אֲבֹתֵיכֶם אֱלֹהֵי אַבְרָהָם אֱלֹהֵי יִצְחָק וֵאלֹהֵי יַעֲקֹב, שְׁלָחַנִי אֲלֵיכֶם; זֶה-שְּׁמִי לְעֹלָם, וְזֶה זִכְרִי לְדֹר דֹּר
appears what can be seen as an old Perush, probably by RJE, as it is necessitated by the merge of E and J. The name revealed in this E fragment, skipping the bold part, is יְהוָה, and in the E context it makes perfect sense. In the J text, however, Hashem's name always was יְהוָה, and therefore the fragment, without the bold part, is quite incomprehensible to readers of the combined text of E and J. In their eyes, Moshe must have been asking for something deeper, for the meaning of the Divine name. And the answer is given in the bold part: אֶהְיֶה אֲשֶׁר אֶהְיֶה. Read more here.In Shemot 6:2-4,
וַיְדַבֵּר אֱלֹהִים , אֶל-מֹשֶׁה; וַיֹּאמֶר אֵלָיו, אֲנִי יְהוָה. וָאֵרָא, אֶל-אַבְרָהָם אֶל-יִצְחָק וְאֶל-יַעֲקֹב--בְּאֵל שַׁדָּי; וּשְׁמִי יְהוָה, לֹא נוֹדַעְתִּי לָהֶם. וְגַם הֲקִמֹתִי אֶת-בְּרִיתִי אִתָּם, לָתֵת לָהֶם אֶת-אֶרֶץ כְּנָעַן--אֵת אֶרֶץ מְגֻרֵיהֶם, אֲשֶׁר-גָּרוּ בָהּ
it is claimed, in a text that seems to come from H, that the name יְהוָה was not known to the fathers. A similar deep problem would seem to arise. The name was known to the fathers! One did not see the problem: P follows the H fragment as a literal instruction. He uses the name יְהוָה only after this fragment, and uses אֵל שַׁדָּי and אֱלֹהִים before. It must be that P wanted to rewrite the Torah without J, and without J there is no problem. The later editor, R, does not relate to the problem. One could maintain that R's answer would be similar to the answer of RJE. The fathers knew the meaning of אֵל שַׁדָּי but they did not know אֶהְיֶה אֲשֶׁר אֶהְיֶה as the meaning of יְהוָה.