This bring about the next part of the verse: “(Lighting up the Menorah) is an eternal law ‘מֵ אֵ ת-from the letters of א through ת’ of the Children of Yisroel,” meaning that the letters of the Torah should cause Aharon to “set up the lamps” of “rejoicing in Mitzvos.”
לִ הְ יוֹ ת וּ מִ זֶּ ה נִ מְ שׁ ָ ך"ַ ת עוֹלָם חוּק מֵאֵת בְּנֵי יִ שְׂ רָ אֵ ל," וֹת הַתּ וֹרָ לִהְ יוֹת אוֹתִ יה גוֹ רֶ מֶ ת שׁ ֶ י אַהֲרֹן אֶת הַנֵּרוֹת ך– בְּחִ ינַת "שִׂ מְ חָ ה שׁ ֶ ל מִ צְ וָ ה,"
This power of the letters is because the letters of the Torah are from the level of Moshe (Chochma of Atzilus), and from that level “you (Moshe/Torah) will ‘תְּ צַוֶּה-connect’ the Children of Yisroel with Hashem.”
וֹת הַתּוֹרָה הֵן הַנִּ מֵחֲמַת כִּי אוֹתִימְ שׁ ָ כ ו ֹ ת מִ בְּחִ ינַת מֹשׁ ֶה – "וְאַתָּה תְּ צַוֶּה אֶת בְּנֵי יִ שְׂ רָ אֵ ל כוּ '".
In other words, when a person humbles himself to Hashem, and he learns Torah, those letters of Torah connect him to Hashem and give him the power to have “rejoicing in Mitzvos.”
