Another interpretation: "I will shoot My words into your mouth like an arrow," for "and I will teach you" [ve-horeitikha] means nothing other than the language of "he shall surely be shot through" [yaroh yiyareh] (Exodus 19:13). And once the Holy One, blessed be He, assured him that He was with him, he accepted upon himself to go, as it is said, "And Moses went and returned to Jether his father-in-law" (Exodus 4:18).
God Promises to Shoot His Words Into Moses Like an Arrow
Yalkut Shimoni on Torah 171:5
דָּבָר אַחֵר, אֲנִי יוֹרֶה דְּבָרַי לְתוֹךְ פִּיךָ כְּחֵץ, וְאֵין "וְהוֹרֵיתִיךָ" אֶלָּא לְשׁוֹן יָרֹה יִיָּרֶה. וְכֵיוָן שֶׁבִּשְּׂרוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁהוּא עִמּוֹ, קִבֵּל עָלָיו לֵילֵךְ, שֶׁנֶּאֱמַר "וַיֵּלֶךְ מֹשֶׁה וַיָּשָׁב אֶל יֶתֶר חֹתְנוֹ".