...לְפִיכָךְ הֶרְאָהוּ הַקָּדוֹשׁ בָּרוּךְ הוּא אֵשׁ בּוֹעֶרֶת וְאֵינֶנּוּ אֻכָּל...
לְפִי שֶׁהָיָה הַקָּדוֹשׁ בָּרוּךְ הוּא מְדַבֵּר עִם משֶׁה וְלֹא הָיָה מְבַקֵּשׁ לִבָּטֵל מִמְּלַאכְתוֹ, הֶרְאָה לוֹ אוֹתוֹ דָּבָר כְּדֵי שֶׁיַּהֲפֹךְ פָּנָיו וְיִרְאֶה וִידַבֵּר עִמּוֹ, שֶׁכָּךְ אַתָּה מוֹצֵא מִתְּחִלָּה וַיֵּרָא מַלְאַךְ ה' אֵלָיו, וְלֹא הָלַךְ משֶׁה, וְכֵיוָן שֶׁבָּטַל מִמְּלַאכְתוֹ וְהָלַךְ לִרְאוֹת, מִיָּד (שמות ג, ד): וַיִּקְרָא אֵלָיו אֱלֹהִים.
...the Holy One, Blessed be He revealed Himself in a thorn-bush that was burning but not consumed...
since the Holy One, Blessed be He was talking with Moses and he did not want stop his task [of minding the sheep], He showed him this thing so he would turn his face and see Him. You find this [intimated] from the beginning [of the verse]: "An angel of the LORD appeared to him" - yet Moses did not go. Once he stopped doing his task and went to see, immediately "God called him" (Exodus 3:4).