Deuteronomy 27:13 - Joseph Benson’s Commentary on the Old and New Testaments

To curse Of the former tribes, it is said, they stood to bless the people: of these, that they stood to curse. Perhaps the different way of speaking intimates, that Israel in general were a happy people, and should ever be so, if they were obedient. And to that blessing, they on mount Gerizim said, Amen! But the curses come in only as exceptions to the general rule: “Israel is a blessed people: but if there be any even among them that do such and such things, they have no part or lot in this matter, but are under a curse.” This shows how ready God is to bestow the blessing: if any fall under the curse, they bring it on their own heads. Four of these are children of the bond-women, to show that the curse belongs to those of servile and disingenuous spirits. With these are joined Reuben, who by his shameful sin fell from his dignity, and Zebulun, the youngest of Leah's children, that the numbers might be equal.