John Calvin Commentary Numbers 13:18

"and see the land, what it is; and the people that dwell therein, whether they are strong or weak, whether they are few or many;" — Numbers 13:18 (ASV)

And see the land what it is. The counsel of Moses had this purpose: that the people might be made aware of how rich and fertile the land was. For a barren country does not support a large population, and the healthfulness of a locality is inferred from the vigor of its inhabitants. He, therefore, chiefly insists on the goodness of the land and its abundant production of fruits.

Still, perhaps, God also intended for the Israelites to be forewarned that they would have to contend with strong and powerful enemies, so that they would not be alarmed and discouraged upon suddenly seeing them. But the main point was that the pleasantness and fertility of the land might allure them to take possession of it.