And the people complained in the hearing of YHVH about their misfortunes, and when YHVH heard it, his anger was kindled, and the fire of YHVH burned among them and consumed some outlying parts of the camp.
Numbers 11:1

Cry out to God in your despair, but don't complain. There is a difference. Nobody loves a complainer. Our speech is important to God because he has imbued it with some of his creative power. When we complain against God, we deny and diminish his power to act in our lives.

The story of the elders prophesying in in this chapter is inserted between stories of the people complaining and God punishing them to mitigate the ill effects of lashon harah. The people spoke lies, so God countered by sending fire to stop the contagion and prophets to speak the truth among them.