After Bnai Yisroel conquered Eiver HaYardern, the tribes of Reuven and Gad approached Moses, saying that they had much livestock, and inasmuch as Eiver HaYardern is rich pastureland, they wished to settle in Eiver HaYardern and were willing to waive their portions in Canaan. Moses rebuked them sharply. "Your brethren will go to battle and you will remain here? Why are you discouraging the nation from going into the land that G-d promised them? This is what your fathers did when they rejected Canaan, resulting in our wandering in the wilderness for forty years. And now you are following in your fathers' footsteps, a society of sinful people." (Bamidbar 32:1-34)
The tribes of Reuven and Gad then explained that they never intended to shirk their responsibilities to conquer Canaan. Rather, they were willing to be the vanguard, and after Canaan is conquered, they would settle in Transjordan.
The obvious question is why was Moshe so severely harsh with them, calling them "as sinful as their fathers," and not giving them the opportunity to explain themselves.
I believe the answer can be found in Moshe's words when he recounts their history. Referring to the tragic episode of the spies, Moshe said, "All of you approached me," (Devarim 1:22). Rashi comments that Moshe was saying, "You approached me as a mob, the young pushing themselves ahead of the old, and the old pushing themselves ahead of the leaders." Essentially Moshe was saying, "I should have known that no good could come out of a venture that was totally lacking in respect."
Let us now look carefully at the narrative in Bamidbar. "The children of Reuven and the children of Gad had abundant livestock." Reuven was the oldest of the tribes, and Gad was much younger. The Torah, therefore, appropriately lists Reuven first. However, when they approached Moshe, "The children of Gad and the children of Reuven came to Moshe, the younger pushing himself ahead of the older. Seeing this lack of respect, Moshe said, "This is a repetition of what happened before," and he accused them of being as sinful as their fathers had been.
Their lack of middos can be further seen from the words of the two tribes, who said, "We will build pens for our livestock and cities for our children," giving priority to their possessions over their families. Moshe corrected them, saying, "Build cities for your children first and then pens for your livestock."
People who are derelict in one middah are often lacking in other middos as well. Ramban, in his famous letter to his son, tells him to begin by bringing his anger under control, and this would then lead to refinement of other middos.
Middos are primary in Yiddishkeit. Rebbe Chaim Vital, the disciple of the Ari z"l said that one must exercise even greater caution with refinement of middos then with than with the observance of mitzvos (Shaar Hakedusha 2:2).
The 613 mitzvos are the building blocks of which a Torah life is constructed. However, a pile of building blocks do not yet make a structure. The middos of Torah are what gives Yiddishkeit its structure.
Editor's Note: for further development of this theme by Rav Dr. Twerski, see Glatt Kosher Is Not Enough and Am I Really Frum?