Tafsiran Ulangan 27:12: Rashi, Chizkuni, Kli Yakar & Rashbam

לברך את העם [THESE SHALL STAND UP …] TO BLESS THE PEOPLE — The procedure was as is found in Treatise Sotah 32a: Six tribes ascended the top of Mount Gerizim and the other six the top of Mount Ebal, the priests, the Levites and the Ark remaining below in the midst (i.e. in the valley between). The Levites turned their faces towards Mount Gerizim and began to recite the blessing: “Blessed be the man that does not make any graven or molten image etc.”, and both these and those (the tribes on Mount Gerizim and those on Mount Ebal) answered “Amen”! Then they turned their faces towards Mount Ebal and began to recite the curse, saying: “Cursed be the man who maketh any graven [or molten image]” — and so in the case of all of them (the curses set forth here) till the last: “Cursed be he that does not uphold [all the words of this law to do them]” (cf. Rashi on Deuteronomy 11:29).

אלה יעמדו, “the following are to stand, etc.;” all the tribes that stood on the mountain listening to the blessings were descended from Yaakov’s principal wives Leah and Rachel. Seeing that Leah had so many sons, they took the oldest and the youngest of these and placed them with the four tribes that were descended from the auxiliary wives. Leah’s oldest son who had been under suspicion of having committed an inappropriate act with one of Yaakov’s auxiliary wives was placed there so that the curse on people sleeping with their neighbour’s, or their father’s wives would be impressed on the descendants of his who heard it.

These shall stand to bless the people, etc. And regarding the curses it does not say “these shall stand to curse,” because the good things come from God in actuality, but the curses only come by themselves through the hiding of His face, may He be blessed, for from the mouth of the Most High, evil does not come forth (Lamentations 3:38). Therefore it says, and these shall stand upon [i.e., for] the curse and not “to curse,” but only to designate the arrival of the curses, and the matter is uncertain whether they will come or not, since they only come through the hiding of [God’s] face, therefore the matter still depends on the indication of the celestial system/arrangement.