Murmuring or complaining is one of those sins that are overlooked.
Sometimes, we get so focused on the "big sins" such as murder and adultery that we overlook this sin.
But the Lord doesn't give this sin a free pass; quite the opposite.
It's a hidden killer! This sin unleashed a plague that killed thousands of Israelites.
The Israelites quickly they forgot their God who had led them out of Egypt with signs and wonders. They had just witnessed His dividing of the Red Sea and destruction of those who had enslaved them.
And yet, so quickly they returned to looking only with their natural eyes at the problem in front of them, completely forgetting the miracle working power of their God!
And so they murmured against Moses.
But honestly, weren't they really murmuring against God...