Here are the immediate circumstances.
They lacked water. They grew very thirsty.
It was a serious matter in those desert sands with human lives, and young children, and the stock.

No, it was not serious: really a very small matter, for God was along, and the enterprise was of His starting. It was His concern, all this strange journey. And they knew Him quite well enough in their brief experience to be expecting something fully equal to all needs with a margin thrown in.

There was that series of stupendous things before leaving Egypt.
There was the Red Sea, and fresh food daily delivered at every man's tent door, and game, juicy birds, brought down within arms' reach, yes, and - surely this alone were enough - there was living, cool water gushing abundantly, gladly out of the very heart of a flinty rock - if such a thing can be said to have a heart!
Oh, yes it was a very small matter to be lacking anything with such a lavish God along.

But they forgot.
Their noses were keener than their memories. They had better stomachs than hearts. The odorous onions of Egypt made more lasting impressions than this tender, patient, planning God. Yet here even their stomachs forgot those rock-freed waters. These people must be kinsfolk of ours. They seem to have some of the same family traits.

Listen: they begin to complain, to criticise. God patiently says nothing but provides for their needs.
But Moses has not yet reached the high level that later experiences brought him. He is standing to them for God. Yet he is very unGodlike.
Angrily, with hot word, he smites the rock.

Once smiting was God's plan; then the quiet word ever after.
How many a time has the once smitten Rock been smitten again in our impatience!
The waters came! Just like God!
They were cared for, though He had been disobeyed and dishonoured.

And there are the crowds eagerly drinking with faces down; and up yonder in the shadow standeth God grieved, deeply grieved at the false picture this immature people had gotten of Him that day through Moses.

Moses' hot tongue and flashing eye made a deep moral scar upon their minds, that it would take years to remove. Something must be done for the people's sake.
Moses disobeyed God. He dishonoured God.
Yet the waters came, for they needed water.

And God is ever tender-hearted.
But they must be taught the need of obedience, the evil of disobedience.
Taught it so they never could forget.