In this chapter, the Israelites need miraculous water again and they fight some Amalekites.
When I talked before about bringing "water out of a rock", I was taking that expression from this chapter, although somewhat ironically. When I said that, I meant it in the way of "doing the impossible", but it's ironic because in this passage that is exactly what happens: Moses does the impossible by bringing water out of a rock.
The previous miracles in the wilderness were bizarre to the point that "manna", the name for the heavenly bread, sounds like the Hebrew for "what is it", a sign of their astonishment at this unexpected food. Bringing water from a rock, however, is truly amazing, because it's such a paradox. Water does not come from rocks, a rock is a hard, dry object that is endemic to their journey in the wilderness. The Israelite people are surrounded by rocks and none of these rocks are helpful to them. Drawing water from a rock is impossible because the rock does not have any water to give you, but here that is exactly what God commands Moses to do. It's more than just a little water, too; there is enough water coming out of this rock that it can satisfy the thirst of approximately two million people, so this must have been a substantial amount of water.
A rock is harsh and unforgiving. A rock was the pillow under Jacob's head when he fled from Esau in Genesis 28, a symbol of his poverty and desperation. However, the same rock became the pillar of his worship for the LORD when he poured oil on it, demonstrating the stability and endurance of his devotion. And not just any rock, Jacob says the same rock that symbolized his poverty would be the monument of his devotion if the LORD would be with him. Now we are faced with the paradox of a rock being the source of sustenance for the Israelite people. This shows that out of the objects that define Israel's hardships he can create a source of nourishment. Perhaps there is also an undertone that this rock also symbolizes the worship of the Israelites, just like Jacob set up his rock as a pillar in the house of God (bethel).
This is the second time the people have quarreled about water (or lack thereof), and we can see the growing tension as Moses says, "A little more and they will stone me". No matter how many times Moses tells the people that God is their true leader, they still appear to blame Moses for all of their situational difficulties.
It's also worth noting that this rock is called the "rock of Horeb" and Horeb is the name of the mountain where God first met Moses back in Exodus 3 when Moses was in exile. Now the people have returned to Horeb and the sign that God gave Moses is about to come true: "When you have brought the people out of Egypt, you shall worship God at this mountain." (Ex 3:12) This also associates the rock that is the source of water with Moses's encounter with the LORD. In the next chapter this place is called the "mount of God", so this rock is part of God's domain. We will read more on this subject later.
Next, the Amalekites come out to fight against Israel. This is the first battle we have seen since Abraham and his men attacked the four kinds in Genesis 14. We previously saw that the LORD wished to take the Israelites through the desert and Red Sea crossing because "when they see war, they might turn back". Now, it appears, war is coming to them and they cannot avoid it. This is a harbinger of things to come, because Canaan is a densely populated land and the Israelites are invaders; everyone will fight to keep them out because the only land they are going to get is land taken from someone else.
In this case, we aren't told why the Amalekites attacked, or even exactly who the Amalekites are. I don't believe they are exactly Canaanites because Israel is still out in the Sinai desert, but we will discover that the nations through which Israel seeks passage are also generally hostile to it, so that's possibly the case here.
Then there's this peculiar note about the "staff of God" being raised up and how that influences the battle. This is a miracle which shows that just as God was able to give Joseph favor and success in whatever he did, God is also able to influence human events here by giving victory to the Israelites. We have already seen something similar in Genesis 14 when Abraham and his 318 trained men were able to defeat an entire army. While not overtly supernatural, it is unexpected enough that I think it warrants mentioning. Combining Abraham's privileged position as a servant of the LORD with the extreme odds that he beat in winning that battle leaves me with a fairly strong belief that it implies supernatural assistance.
Here, however, it is more than implied: we are told that victory or defeat depended entirely on whether the "staff of God" was raised over the battle or lowered. In this act, Moses enlists the aid of two of his top leaders, Aaron his brother and Hur. Aaron is well known, but Hur is rarely mentioned again in the bible. We see people with the same name, but it is difficult to tell if it's the same Hur or a different man with the same name.
After a victory, Moses constructs an altar. Two chapters ago the LORD declared himself the healer of Israel. Here Moses declares him the "banner" of Israel, as their captain and symbol of military prowess. They will need that when they get to the promised land, and this chapter foreshadows all of this.