(Telling the story to a school class many centuries later, a teacher whose English was not yet very good spoilt it by talking about “the twelve spices”, thoroughly confusing the children!)
Because ten of the twelve spies brought back a pessimistic report, God decreed that that generation had to die out in the wilderness. The ten pessimists deserved to be punished, that we can understand. But the Israelites as a whole – what was their sin? They were only following a lead!
The Malbim says that the spies were sent out because of the pressure exerted by the people. Moses rebukes the people in D’varim 1:22: “And you approached me, every one of you, and said, ‘Let us send men before us…'”.
It all seems very democratic, and it is even more so when we reflect that one spy came from each of the twelve tribes. But each spy was inevitably concerned for his own tribe’s interests. There was little likelihood that they would look at the land on its merits and bring back an objective report. Moses must have realised this, so why did he go along with the people’s wishes in the first place?
The Midrash suggests that though God said, Sh’lach-l’cha anashim, “Send men for yourself“, this was not an actual command; what it implied, as Rashi points out, was “Send men if you yourself so desire”.
A good leader is in touch with his people and does not ignore their wishes, but by going along with the people’s pressure Moses did not sufficiently acknowledge the danger that the spies would promote parochial, tribal interests. He did not brief them adequately to ensure they would rise above the selfish and self-serving.
Only Joshua and Caleb sensed what was good for the nation as a whole and what would accord with the Divine plan.