The people had complained and tested the LORD by asking, "Is the LORD really with us?" So Moses named that place Massah, which means "testing" and Meribah, which means "complaining."
Then Moses told Aaron, "Grab your fire pan and fill it with hot coals from the altar. Put incense in it, then quickly take it to where the people are and offer it to the LORD, so they can be forgiven. The LORD is very angry, and people have already started dying!"