Dying of thirst
Israel had escaped Egypt and was crossing the desert. There was no water. The people were dying and turned on Moses. God gave him an unusual command:
"Behold I will stand there before thee, upon the rock Horeb: and thou shalt strike the rock, and water shall come out of it that the people may drink. Moses did so before the ancients of Israel."
Exodus 17:6
The rock was struck once. Life poured out of it for the whole nation.
The second rock
Years later, near the end of the journey, the same thing happened again. No water, and the people angry. But this time God's instruction was different:
"Take the rod... and speak to the rock before them, and it shall yield waters."
Numbers 20:8
Speak to it. Not strike it.
Moses was furious with the people. He raised his rod and struck the rock twice. The water still came. But God's response was severe:
"And the Lord said to Moses and Aaron: Because you have not believed me, to sanctify me before the children of Israel, you shall not bring these people into the land, which I will give them."
Numbers 20:12
After forty years of leading Israel, Moses was barred from the promised land. For striking a rock twice. Why would that matter so much?
The rock was Christ
Paul gives the answer:
"And all drank the same spiritual drink: (and they drank of the spiritual rock that followed them, and the rock was Christ.)"
1 Corinthians 10:4
The rock was a picture of Christ. And Christ was to be struck once, and only once:
"So also Christ was offered once to exhaust the sins of many."
Hebrews 9:28
Struck once, on the cross. After that, he never needs to be struck again. You only need to speak to him, and the water comes.
Moses broke the picture. He struck the rock a second time.
Living water
On the cross, the rock was struck. A soldier's spear opened Jesus' side, "and immediately there came out blood and water" (John 19:34).
Jesus had already said what that water was:
"If any man thirst, let him come to me, and drink."
John 7:37
And to a woman at a well: "the water that I shall give him, shall become in him a fountain of water, springing up into life everlasting" (John 4:14).
Why this is a big deal
A dying people in the desert. A rock struck once, and water for everyone. Then a second rock, to be spoken to, not struck, and a great prophet who lost everything for getting it wrong.
Fourteen hundred years before the cross, God was already teaching what it would mean. Christ struck once. And after that, whoever is thirsty only has to ask.