Deuteronomy 27:11

11.And Moses charged the people the same day. In order that both the promises and threats might have more efficacy in affecting the minds of all, God enjoined not only that they should be proclaimed in a solemn rite, but also that they should be approved by the people in a loud voice, and sealed, as it were, by their consent. It is elsewhere recorded that this was faithfully performed by Joshua. ( Joshua 8:33.) Let it suffice to say at present that they were all summoned, and conducted before God to subscribe to them, so that henceforth all subterfuge might be put an end to. The tribes of Israel were divided into two parties, that they might stand opposite to each other, and that the blessings might sound forth from one side, and the curses from the other, (196) like ἀντίστροφοι. I confess I do not know why the descendants of Simeon, Levi, Judah, Issachar, Joseph, and Benjamin, were chosen by God to proclaim the blessings, rather than the others; (197) for there is no force in the opinion of the Hebrew writers that those who descended from free mothers were placed in the post of highest dignity: since the tribe of the first-born, Reuben, was united with some who sprang from the bond-maids; unless, perhaps, we may say that the descendants of Reuben were degraded into the second class as a mark of ignominy; but, since both the blessings and curses were offered in the name of the whole people, it is not a point of much importance. For, if this division (198) was made to bear witness to their common consent, it was equivalent to their all alike confessing that the transgressors of the Law were accursed, and those who kept it blessed; and consequently I am not very curious to know why, in their common office, God preferred some to the others. Moses will elsewhere relate that the tribes, which are here separated, were then united together. It would perhaps be a probable conjecture that God, who well knew what would hereafter be the inheritance of every tribe, placed them severally in that station which would correspond to their future allotment.

In order that the sanction might have more solemnity, God chose that the Levites should dictate the words as if He Himself spoke from heaven; for, since they were appointed to be the expounders of the Law, as it behooved them faithfully to repeat what God had dictated out of His own mouth, so they were heard with greater attention and reverence.