Another interpretation of "My strength and song is the LORD" (Exodus 15:2): To what may the matter be compared? To a king who had a single pearl. His son came and said to him, "Give it to me." He said to him, "It is not yours." The son pressed him hard, and he gave it to him. So too Israel: they sang the song, "My strength and song," and they were asking the Holy One, blessed be He, to give them the Torah. He said to them, "It is not yours; it belongs to the celestial beings." Once they pressed Him for it, He gave it to them, as it is said, "The LORD will give strength to His people" (Psalms 29:11).
The King Who Yielded His Pearl and the Gift of Torah
Yalkut Shimoni on Torah 244:5
דָּבָר אַחֵר עָזִּי וְזִמְרָת יָהּ, מָשָׁל לְמַה הַדָּבָר דּוֹמֶה, לְמֶלֶךְ שֶׁהָיָה לוֹ מַרְגָּלִית אַחַת, בָּא בְּנוֹ וְאָמַר לוֹ תֵּן אוֹתָהּ לִי, אָמַר לוֹ אֵינָהּ שֶׁלְּךָ, הִטְרִיחַ עָלָיו וּנְתָנָהּ לוֹ. כָּךְ יִשְׂרָאֵל אָמְרוּ שִׁירָה עָזִּי וְזִמְרָת וְהָיוּ מְבַקְּשִׁין מֵהַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁיִּתֵּן לָהֶם אֶת הַתּוֹרָה, אָמַר לָהֶם אֵינָהּ שֶׁלָּכֶם, שֶׁל עֶלְיוֹנִים הִיא, כֵּיוָן שֶׁהִטְרִיחוּ עָלָיו נְתָנָהּ לָהֶם, שֶׁנֶּאֱמַר (תהלים כט, יא) "ה' עֹז לְעַמּוֹ יִתֵּן".