Charles Spurgeon Commentary Numbers 11:1

"And the people were as murmurers, [speaking] evil in the ears of Jehovah: and when Jehovah heard it, his anger was kindled; and the fire of Jehovah burnt among them, and devoured in the uttermost part of the camp." — Numbers 11:1 (ASV)

And when the people complained, it displeased the LORD:

Interpreters cannot discern what they had to complain of. The curse of labor had been removed; they did not earn their bread with the sweat of their face, for it fell from heaven every day. They were at no expense for clothing; and though they journeyed, their feet did not swell.

I suppose that they complained of the weather. It was too cold; it was too hot; it was too wet; it was too dry. They complained when they stood still; they were much too long in a place. They complained when they marched; they moved too often.

In fact, they were very like ourselves; they often complained most when they had least to complain of. Discontent is chronic to our humanity; and I do not believe that the poorest are the most discontented. It is often the very reverse.

When a man is put in a place where he has nothing to complain of, especially if he is an Englishman, he feels quite out of place. He must have something to grumble at, something or other to be a grievance, or else he is not happy. When the people complained, it displeased the Lord.

And the LORD heard it; and his anger was kindled; and the fire of the LORD burnt among them, and consumed them that were in the uttermost parts of the camp.

He could hear their first murmurings, as they were new to the wilderness, they were hungry, they were thirsty, and the Lord pitied them. But now, when there was no reason for their complaining, his fire in terrible judgment visited his people, on account of their rebellion and murmuring against the goodness of God.