The people continue the trek through Sin, following cloud and fire as they went (likely how we should understand that “…according to the commandment of the Lord” bit. They camp at Rephidim, just a bit further south and the last stop prior to Mt. Sinai. Wouldn’t you know it, there’s no water there for the people to drink. Given that they followed the fire and cloud to Rephidim and harvested free honey flakes from the heavens every morning since they left, you’d think these fellas would put two and two together and perhaps ask the Lord to provide for water (you know, like He’s already done once.)
But no, instead, they quarrel with Moses and demand to be given water to drink. In this, they ignore not only how God has provided but Moses’ entreaty just days ago that their beef is with YAHWEH, not him and Aaron. They persist nonetheless, once again protesting that they could have died of thirst in Egypt without all this travel and said among themselves, “Is the Lord among us or not?” This is outright foolishness. God’s patience with them is remarkable.
Even Moses gets in the act this round. Note how he protests to the Lord, “What shall I do with this people? They are almost ready to stone me.” He’s losing his nerve a bit. I get it, but he’s not exempt from cloud, fire, honey flakes, magic water log, and free quail. He’s leading this circus, the person leading folks around has to hold the whims back as a good example.
Even in the face of all this, God provides. He instructs Moses to walk in front of the people and the elders of Israel with the same stick that turned the Nile to blood and strike a rock to get water to come out. This is a level up from taking existing water and making it sweet, this is a river flowing from a stone. The people need to see it. The elders need to see it. It goes done as the Lord instructed. Moses, though, doesn’t want them to forget how they’ve behaved and names the place both Massah and Meribah, which means “testing” and “quarreling” respectively.
Directly after this incident, Amalek attacks Israel at Rephidim. Perhaps, word has gotten around that a wandering band of Hebrew malcontents are ripe for the pickin’ on the outskirts of the desert. Moses instructs Joshua to find some fellas to go fight with Amalek (apparently it wasn’t a sneak attack). The sense is, Joshua may have a hard time rousting up qualified folks, but he’s the man to make it happen.
However, it doesn’t particularly matter, this will be God’s victory. Moses goes to the top of the hill at the battle, Nile/water stick in hand. Whenever he holds up the staff, the Israelites win. When he drops the staff down, they start to lose. Understandably, Moses’ arms get tired (he’s a human after all). On the bright side, Aaron and Hur hang around and help him hold up is arms (this has all the makings of a pamphlet for a men’s retreat).
And it works, Joshua overwhelms Amalek. The victory is obviously God’s, but often history attributes it to the leader, thus the attribution to Joshua. Afterwards, God has Moses record the victory for the annals and to keep it in the ears of Joshua. Just like the water from the rock, God’s intervention on His people’s behalf needs to be remembered (especially for a people so prone to forget things that happen right in front of them).
Moses builds an altar to commemorate the victory and proclaims a generational war with Amalek (rough times for him).