Musar к Бамидбар 13:2

Another difficulty is: What was Israel's sin in asking for these spies to be sent out? Our sages claim that G–d tripped them up intentionally, since they should never have demanded such a mission. Furthermore, why is the fact that Israel initiated this mission by asking Moses to send spies, not reported here but only when Moses summarizes the events of the forty years before his death? (Deut. 1,22). Another problem is why several descriptions of the spies' mission are used such as לתור, לרגל, and לחפור. Besides, why did Moses have to send out twelve spies, would not two spies have been sufficient just as when Joshua sent two spies to Jericho?