Números 2

Números 2:33

We gather from the book of Numbers that there may be something greater than Israel too. For there the whole of Israel is numbered and reckoned in twelve tribes, as under a fixed number. But the tribe of Levi, being of greater eminence than the others, is accounted extra to this number and never thought of as being one of Israel's number [of twelve]. — COMMENTARY ON THE SONG OF SONGS, PROLOGUE