Quote from What More Can God Say by Ray Stedman:
“The people of that (Moses’) day thought God wanted them to keep these Ten Commandments as the only way they could please Him. They felt He demanded a rigid, careful, scrupulous observance of the Ten Commandments. But what they did not understand, though God pointed this out to them many times, was that God never expected them to keep it. He knew they could not. He did not give it to them to be kept … He gave it to them to show them they could not keep it, so they would be ready to receive a Saviour. But with presumptuous confidence they tried to keep it and when they could not… they pretended to keep it, just as we do today.”
Grace is hard to accept, both then and now.