In this chapter, Moses tells the people more about the Feast of Unleavened Bread and the Israelites depart from Egypt, heading towards the Promised Land.
Before I get into the theological analysis, I should point out some textual notes. This chapter is somewhat redundant with what we read in chapter 12, in particular with the discussion of the unleavened bread. What happened in chapter 12 was God telling Moses the ordinances of eating unleavened bread, but Moses never told the people. They ate unleavened bread because they were forced to flee Egypt. In this chapter, Moses is now telling the people that they must celebrate the Feast of Unleavened Bread. So the information is going through a couple stages which are each described once, but that means the information is repeated twice. Oral traditions.
We also see Joseph's wishes (expressed in Genesis 50) are honored by the people, as they take his bones up with them.
With that out of the way, I want to discuss the redemption of the firstborn. The principle here is simple enough: God killed all the firstborn of Egypt, but he spared the firstborn of Israel. Since the firstborn of Israel were spared, they now belong to the LORD as a possession of sorts and must be either sacrificed to him or redeemed through the sacrifice of another. Of course, the reason the Israelite firstborn now belong to the LORD is not just because he spared them, but because he paid for them. This is another reason why I say that the Passover must be a memorial to some other event, because the lambs that were sacrificed were the Israelite's own property, so they were just trading one thing to die for another. So in what way is the LORD owed anything by the Israelites, if the Hebrews performed this alternate sacrifice? They could reasonably argue they paid their dues, albeit the cost of a lamb is less than the cost of a son. In order for this to make sense (in my opinion), the LORD must have performed some other substitutionary sacrifice on behalf of the Israelites, and thus it is due to the LORD's sacrifice that he now has a right to the Israelite firstborn. Of course, the text doesn't say this, but then the text doesn't exactly explain why the Israelites must sacrifice the firstborn of their animals and redeem the firstborn of their sons. Ostensibly it is a memorial to when the LORD brought them out of Egypt: verse 16, "it shall serve as a sign on your hand and as phylacteries on your forehead, for with a powerful hand the LORD brought us out of Egypt."
However, what is left unexplained (in my opinion) is this segment of verse 12: "the males belong to the LORD." This is much stronger than a simple memorial, this is a statement of the LORD's ownership of the firstborn. This is not part of the Abrahamic Covenant as we saw it defined before, which simply stipulated the obedience and homage of Abraham and his seed in exchange for divine protection and provision. So while the text doesn't exactly say it, in my opinion there is a subtle but important transition happening here, as the Israelites are no longer regarded merely as a vassal to their divine lord, but now they are regarded as a possession which was redeemed from a formerly certain destruction. We will see the Pentateuch expand on this theme later, but I want to point out that it (partly) has its roots here in this chapter.
On a more practical note, there is a provision for redeeming donkeys because donkeys generally breed less than sheep and goats and grow slower, and are therefore much more expensive. It would be a heavy cost to poorer Israelites to sacrifice their firstborn donkeys. There is a similar (but mandatory) process for redeeming one's firstborn sons. Also note that donkeys shall not be sacrificed, but rather have their necks broken if not redeemed. This is because donkeys are ritually unclean, and therefore cannot be offered as a sacrifice.
Also remember that the firstborn son is a metaphor for strength and power, being the proof of the virility of the father and fertility of the mother, as well as the future heir of the father's wealth. So the consecration of the firstborn unto the LORD is a metaphor for giving the LORD your very best and strongest as a sacrifice. This is a persistent theme throughout the rest of the Pentateuch.
We have also seen three different passages that say something like, "you shall tell your son" or "when your son asks you what this rite means". Obviously the emphasis is on passing down knowledge from generation to generation and teaching one's sons to follow the LORD, but also in these statements we see shadows of the oral traditions behind the Pentateuch. The reason a father has to tell his son is because they don't have it written down for the son to read. There have been three of these statements, which are directed about: the Passover (sacrifice of the lamb), the Festival of Unleavened Bread and removal of yeast from one's home (verse 8) and the redemption of the firstborn (verse 14). While these statements are the result of different activities (the sacrifice, the festival, the redemption of the firstborn), all of them generate very similar "explanations", which is perhaps why they are so easy to confuse: all of them relate specifically to the Passover of the Israelites and their rescue from slavery in Egypt.
From my perspective, I can understand why they would celebrate the Passover and practice the redemption of the firstborn. These seem like really critical elements to the story and what's going on spiritually as well. It's strange to me that there is so much emphasis on the unleavened bread. In context, the removal of yeast is simply due to the haste of the Israelites in their departure: their departure was unexpected and they were unprepared. I know that, in general terms, yeast is considered a metaphor for sin, and thus unleavened bread is a reference to purity. But the text here does not explain that at all, and refers primarily and repeatedly to the notion of haste and unpreparedness, always with reference to the Israelite's sudden departure from Egypt. I can't think of any interesting or novel interpretation of how this relates to other parts of the bible, so.... yeah. I'll come back and fill this part out more if I think of something later. Of course, the reason I'm looking for something is that the Feast of Unleavened Bread is really important to the Hebrew traditions. It's one of the three main feasts that they celebrate. We will see it referred to again, so maybe we will discover more about it in time.
When the people depart Egypt, we see God take them towards the wilderness instead of along the more populated coastline of the Mediterranean, which would be the shortest path to Canaan (and also probably the easiest, with more water and food sources available). Instead, they are taken towards the wilderness of the Sinai Peninsula and towards the Arabian desert.
Verse 21 is also the first appearance of a new manifestation of the LORD: a pillar of smoke or clouds by day, and a pillar of fire by night. As always, I urge my readers to dwell on the various manifestations of the LORD. Whenever we see a new manifestation, often it is because the LORD is trying to convey some new dimension of his personality or characteristics. In some ways, these manifestations are really the core of what the bible is about, which is conveying the nature of God to people in a way that we can understand. The manifestation is a physical representation of that divine nature.
One way to understand the divine manifestations is to consider them as a reflection of what is happening to Israel (or in broader terms, the people of God); that is, God crafts his manifestation as an answer to their need. This is not always true (for instance, the transcendentalism of Ezekiel 1 can hardly be considered an answer to some Israelite need), but it is definitely a major theme throughout much of the bible, including here. Earlier in Exodus, we saw God appear as a burning fire in a bush, supernatural and everlasting, unleashing miracles to bring freedom to his people. He was revealed in this case as both strong (defeating the mighty Pharaoh and the gods of Egypt like Ra) and the redeemer of the Israelites, protecting them from the plagues.
In the case that we are seeing now, his form is transitioning because the needs of the Israelites are also changing. However, the Israelites are not yet out of Egypt so I will return to this topic in just a short while, because we will see the pillars of fire and cloud appear later as well. Up next, we get to see one of the most famous miracles in the entire bible.