Rashi on Deuteronomy 33:8:1-4

וללוי אמר. וְעַל לֵוִי אָמַר: וללוי אמר means AND OF LEVI HE SAID (not to Levi).

תמיך ואוריך. כְּלַפֵּי שְׁכִינָה הוּא מְדַבֵּר: תמיך ואוריך THY THUMMIM AND URIM — He is addressing God (not Levi).

אשר נסיתו במסה. שֶׁלֹּא נִתְלוֹנְנוּ עִם שְׁאָר הַמַּלִּינִים: אשר נסיתו במסה WHOM THOU DIDST TRY WITH TRIALS — [Since this is said in praise of the Levites] we may gather from it that they did not murmur together with the other tribes.

תריבהו וגו'. כְּתַרְגּוּמוֹ. דָּ"אַ — תריבהו על מי מריבה, נִסְתַּקַּפְתָּ לוֹ לָבֹא בַעֲלִילָה, אִם מֹשֶׁה אָמַר שִׁמְעוּ נָא הַמֹּרִים, אַהֲרֹן וּמִרְיָם מֶה עָשׂוּ? (ספרי): תריבהו וגו׳ THOU DIDST STRIVE WITH HIM [AT THE WATERS OF MERIBAH] — Understand this as the Targum has it: (“Thou didst put him to the test”). — Another explanation of תריבהו על מי מריבה: Thou didst seek an occasion against him to come with a pretext, for if Moses said, “Hear now, ye rebels”, what sin did Aaron and Miriam commit? (why were they not allowed to enter the land?) Sifrei Devarim 349:3).

האמר לאביו ולאמו לא ראיתיו. כְּשֶׁחָטְאוּ בָעֵגֶל וְאָמַרְתִּי "מִי לַה' אֵלָי" (שמות ל"ב), נֶאֶסְפוּ אֵלַי כָּל בְּנֵי לֵוִי וְצִוִּיתִים לַהֲרֹג אֶת אֲבִי אִמּוֹ וְהוּא מִיִּשְׂרָאֵל אוֹ אֶת אָחִיו מֵאִמּוֹ אוֹ בֶן בִּתּוֹ, וְכֵן עָשׂוּ. וְאִי אֶפְשָׁר לְפָרֵשׁ אָבִיו מַמָּשׁ וְאָחִיו מֵאָבִיו וְכֵן בָּנָיו מַמָּשׁ, שֶׁהֲרֵי לְוִיִּים הֵם, וּמִשֵּׁבֶט לֵוִי לֹא חָטָא אֶחָד מֵהֶם, שֶׁנֶּאֱמַר (שם) "כָּל בְּנֵי לֵוִי": האמר לאביו ולאמו לא ראיתיו WHO SAID TO HIS FATHER AND TO HIS MOTHER, I HAVE NOT SEEN HIM — When they sinned in the matter of the golden calf and I said, “Who is on the Lord’s side, let him come to me” (Exodus 32:26), all the sons of Levi gathered themselves unto me, and I ordered them each to kill his mother’s father, he being an ordinary Israelite, or his brother on the mother’s side, or the son of his daughter whose husband was an ordinary Israelite, and thus did they do. — It is impossible to explain the term “his father” literally, and “his brothers” as being those on his father's side, and similarly to understand “his sons” literally, for really all these are Levites, and of the tribe of Levi no one sinned., as it is said, “[And there gathered unto me) all the tribe of Levi” (Sifrei Devarim 350:1, Yoma 66b).

כי שמרו אמרתך. "לֹא יִהְיֶה לְךָ אֱלֹהִים אַחֵרִים" (שמות כ, ב): כי שמרו אמרתך BECAUSE THEY KEPT THY WORD, viz., Thou shalt have no other gods,

ובריתך ינצרו. בְּרִית מִילָה, שֶׁאוֹתָם שֶׁנּוֹלְדוּ בַּמִּדְבָּר שֶׁל יִשְׂרָאֵל לֹא מָלוּ אֶת בְּנֵיהֶם, וְהֵם הָיוּ מוּלִין וּמָלִין אֶת בְּנֵיהֶם: ובריתך ינצרו AND THEY GUARDED THY COVENANT viz., the covenant of circumcision (Sifrei Bamidbar 67 on בהעלתך); For the [ordinary] Israelites who were born in the desert did not circumcise their sons, whereas the Levites were [not only] circumcised themselves, [but they] also circumcised their sons.

יורו משפטיך. רְאוּיִין אֵלּוּ לְכָךְ: יורו משפטיך THEY MAY TEACH THY JUDGMENTS (the emphasis is to be placed on “they”) — they alone are worthy of doing this (cf. Onkelos).

וכליל. עוֹלָה (יומא כ"ו): וכליל — means burnt-offering (which was entirely (כליל) burnt on the altar) (Sifrei Devarim 351:3).