There is really nothing more that needs to be expounded on in the main theme of the Parsha. No greater lesson can really be learned by expounding, rather than just looking simply at what happened.
The Jews were on the cusp of entering Israel. Any day now and they would be there. They just received the Torah. All cylinders were clicking and everything was going great. They start complaining and decide they need to send in spies to scout out the land. All they see is the bad, whether real or made up.
After they witnessed all the miracles of the dessert, did they really not think Hashem could help them conquer and settle the Land? Yet they spoke badly of the Land of Israel. They tried to dissuade the people from entering and building up the land.
The lesson is clear. We often hear people disparaging Israel. Be it the weather or the politics or the attitudes or the people or whatever. We have to see the good in Israel. Sure, we have to see the bad and try to improve it. But that would be looking at the bad with an eye to improve, rather than an eye to complain and disparage. Don't harp on the bad. See the good and encourage Aliyah, rather than discourage it.