God promised that the Land he would bring us into was good. Exodus 3:8:
and I am come down to deliver them out of the hand of the Egyptians, and to bring them up out of that land unto a good land and a large, unto a land flowing with milk and honey; unto the place of the Canaanite, and the Hittite, and the Amorite, and the Perizzite, and the Hivite, and the Jebusite.
Yet despite this assurance, the spies were instructed by Moses to assess whether the Land was good. Numbers 13:17-20:
And Moses sent them to spy out the land of Canaan, and said unto them: 'Get you up here into the South, and go up into the mountains;and see the land, what it is; and the people that dwelleth therein, whether they are strong or weak, whether they are few or many; and what the land is that they dwell in, whether it is good or bad; and what cities they are that they dwell in, whether in camps, or in strongholds; and what the land is, whether it is fat or lean, whether there is wood therein, or not. And be ye of good courage, and bring of the fruit of the land.'--Now the time was the time of the first-ripe grapes.--
Given that God had already promised us a "good land" (large, and flowing with milk and honey), why did Moses require that the spies inspect whether the Land was "good or bad"?