During the blessings and curses in parashas Ki Tavo, why were Reuven and Zevulun, in particular, sent to Mount Ebal? (They were the only two tribes descended from Rochel and Leah who were sent to that mountain.) Reuven in particular seem like they should have merited to be on the "good" mountain, a.k.a. Mount Grizim.
Rav Hirsch explains on verse 12 and 13 that the nation was to be divided in half, and there were 6 sons of Leah and 2 of Rachel (the main wives) and 4 children of Bilha and Zilpah (the maid servants). Thus two of them had to be moved to the other mountain. The question then becomes, Why were Reuven and Zevulun the two that were moved?
Rav Hirsch explains:
When reckoning up the tribes, as in Ex. 1, 2-4, the eight sons of Leah and Rachel are placed together (Joseph is missing there as he was already in Egypt) and then come the four sons of Bilha and Zilpa. Here the nation is to separate into two halves to have the Levites in the middle, so two of the eight have to be transferred to the other four. Now, to avoid any appearance of difference of rank in the two halves the tribes of the eldest and youngest of the sons of Leah, Reuben and Zebulun were to join those of Bilha and Zilpa. Hence the grouping:- Simon, Levi, Judah, Issachar, Joseph and Benjamin on the one side, and Reuben, Gad, Asher, Zebulun, Dan, and Naphtali on the other. But also to avoid the slightest appearance of the קללה being said over the group of the בני השפחות, these were given their position just on Ebal so that the קללה pronouncements were made not to seem to be directed at them but to come from them. They were those that עומדים על הקללה and from the side of the בני אמהות the ברכות were directed at them. (But of course, as explained above both the blessing and curse were said as coming from the whole twelve tribes I.L.)