What does Numbers 20:8 mean?

'Take your staff, gather the people together—you and your brother Aaron. Speak to that rock in front of them, and it will pour out water. You'll bring water out of the rock for everyone and their animals to drink.' Numbers 20:8 - Modern Text Bible

(God tells Moses to speak to the rock, not strike it. This is a test of trust and obedience. God wants to provide for the people, even when they're complaining.)