The Rebbe says:
1. This week’s Torah portion tells us how the Tribes of Re’uvain and Gad had an extraordinarily large amount of livestock and they wished to remain in the lands that the Bnei Yisroel (the children of Israel) had just conquered, rather than crossing the Jordan River with their brothers into the Land of Canaan. They came to Moshe Rabbeinu (Moses our teacher) and said, “This land which G-d defeated in front of the congregation of Israel is a land suitable for livestock and your servants have a lot of livestock. If it finds favor in your eyes, let this land be given to your servants as a heritage. Do not take us across the Jordan”.
Moshe Rabbeinu’s initial answer to this was, “Your brothers should go to war while you stay here?! Why are you discouraging the children of Israel from crossing over to the Land which G-d has given them? This is exactly what your fathers (the spies) did when I sent them from Kadesh-Barne’a to explore the Land. They went up to the Valley of Eshkol, saw the Land, and then they discouraged the children of Israel from crossing into the Land which G-d has given them”.
The Tribes of Re’uvain and Gad responded and said to Moshe Rabbeinu, “We’ll arm ourselves quickly and go ahead of the children of Israel and fight until we’ve brought them to their place. We’ll not return to our homes until each member of the children of Israel has taken possession of his inheritance”.