פרשת וזאת הברכה תשט"ז - הברכה ללוי

And of Levi he said: Thy Thummim and Thy Urim be with Thy holy one, Whom Thou didst prove at Massah, With whom Thou didst strive at the waters of Meribah;

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.

Who said of his father, and of his mother: ‘I have not seen him’; Neither did he acknowledge his brethren, Nor knew he his own children; For they have observed Thy word, And keep Thy covenant.

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).

Who says … [singular] “The tribe” is the subject of the verb. The reference is to, e.g., Samuel, who came to train in the House of God as soon as he was weaned [I Samuel 1: 22].