The latter part of Parashat Matot (chapter 32) tells of the request made by the tribes of Reuven and Gad to colonize and permanently settle the territory of the east bank of the Jordan River, which Benei Yisrael had recently captured from the Emorites. Moshe initially criticizes their request, comparing these tribes to the generation of the meraglim (scouts) who refused to enter the Land out of fear of confrontation with its Canaanite inhabitants. Reuven and Gad clarified that they were prepared to join their brethren in battle against the Canaanites across the river, after first building homes and barns for their families and cattle. Only after the nation's successful conquest of Eretz Yisrael proper would they return to their homes east of the Jordan.
Moshe grants these tribes' request, emphasizing that their right to settle east of the river depended on their participation with the other tribes in the conquest of Eretz Yisrael. He concludes, "Go and build cities for your children and sheepfolds for your flocks, and abide by that which left your mouths" (32:24). This concluding remark requires some explanation. Moshe had already established that the tribes' permanent settlement east of the river depends on their participation in the battles west of the river. Why does he now instruct them to build homes and barns, and why must he reiterate "and abide by that which left your mouths"?
A partial explanation appears in the Midrash Tanchuma (7; this appears as well in Bamidbar Rabba 22:9), which notes that Moshe first mentions the construction of "cities for your children," and only then "sheepfolds for your flocks." Earlier, when Gad and Reuven express their willingness to join the other tribes in battle, they mention that they will build "sheepfolds for our flocks here, and cities for our children." The Midrash charges that Reuven and Gad afforded priority to their wealth and assets over their children; they assigned primary status to their finances, and secondary status to their children. Moshe therefore sought to correct their mistake by restructuring the sequence of events. He told them they must first care for the needs of their families, and only then devote themselves to the well being of their flocks.
This easily explains the first half of this verse – "Go and build cities for your children and sheepfolds for your flocks." Moshe here seeks to correct the misplaced priorities of these two tribes. Why, however, must he reiterate, "and abide by that which left your mouths"?
The Ketav Sofer suggests that this final clause should be read not as an imperative, but rather as the result of the preceding clause. Reuven and Gad's disproportionate focus on their wealth aroused not only Moshe's criticism, but also his suspicion. Moshe understood that people who are so passionately driven after money cannot necessarily be trusted. He therefore ordered them to first build cities for their children and then sheepfolds for their flocks, to demonstrate their reassessment of their priorities, that they understand the secondary status of wealth in their lives. Only then, after they have corrected this error, could Moshe rest assured that they will "abide by that which left your mouths." So long as they emphasized their cattle over their families, giving priority to their financial endeavors, Moshe felt uneasy about their promise to join the rest of the nation in battle. Only once they demonstrated a more balanced perspective and priority scale did he feel confident that they would indeed live up to their commitment and fulfill their promise to participate in the battle in Canaan.
Courtesy of Yeshivat Har Etzion - www.etzion.org.il