In this chapter, the LORD restates the Sabbath of the seventh year and institutes the year of Jubilee.
The first part of this chapter is a restatement of the Sabbath on the seventh year. This was first instituted back in Ex 23:10-11, so I wrote some comments about it back in my corresponding commentary. In brief, this technique helps to maintain soil fertility and it again demonstrates a subtle shift towards permanent farming over nomadic pastoralism. Also in Exodus 23, we are given an implied connection between the rest on the seventh year and the rest on the seventh day, at the end of every week. As with the land, a major part of why people and animals must rest on the seventh day is to rejuvenate and strengthen themselves to resume their labors. It also harkens back to life before the curse of Adam turn work into a laborious burden and the land was corrupted into "thorns and thistles". Though it is not stated in this portion of the chapter, there is also a release from bondage for all Israelite slaves and hired servants at the end of every seven years (Ex 21:2).
This chapter adds a bit more detail how the Sabbath of years works. Namely, the people are commanded to neither sow nor reap. However, they are allowed to go out to their fields and eat grain and fruit directly in the fields. That's what v. 6 and 7 mean when they say that "you shall have the Sabbath of the land for food" (or whatever translation you use). It's a bit confusing for us, but the idea is pretty clear. You can go out and eat whatever you want, but you cannot reap it (i.e. sweep through and gather everything into baskets or storehouses).
The second part of the chapter is new and much more substantial, it is basically a Sabbath of Sabbaths, which is declared the year of Jubilee (Hebrew "truah", meaning "clamor", "acclamation", "a blowing of trumpets", "rejoicing"). Surprisingly, this "blowing of trumpets" is to occur on the day of atonement, Yom Kippur, rather than (for instance) Rosh Hashanah, the traditional festival of trumpets. It surprises me because Yom Kippur is a traditional day of mourning when the high priest announces all of the sins of the people over the "scapegoat". It is a commanded day of fasting (Lev 23:27) and prayer, and among other things, fasting is symbolic of grief in the OT. To make this day the day of "clamor", "blowing of trumpets" and "rejoicing" runs contrary to the typical meaning of the day.
Perhaps that's the point. I wonder if the Jubilee is on Yom Kippur to teach the people that the fasting, sacrifices and prayer are all for a reason, which is the freedom and restoration that typifies Jubilee. Just a thought.
The seven Sabbath of years is similar to the seven Sabbaths of days between the Passover and the Feast of Weeks. I'm not sure if this is intentional, because other than the 50 days/years, there is no apparent similarity between the Jubilee and the Feast of Weeks (they seem to be generally quite different).
The big theme of the Jubilee is that everyone is to "return to his own property". That is, any sale of land is to be regarded as temporary and reverts to its original ownership every 50 years. The bulk of this chapter is covering various details and special cases associated with this rule. For instance, v. 13-17 insists that you must pay less money the closer you get to the Jubilee, under the assumption that if you pay full price for the land, it is because you are expecting to keep it a long time and not give it back. That's why the author insists you must pay less money closer to the Jubilee, and when it says "you shall not wrong one another", the "wrong" would be to pay full price for the land and not give it back during the Jubilee. This is generally the same principle as what we see towards the end of the chapter, that "in proportion to his years he is to refund the amount for his redemption" (v. 52).
Verses 20-22 is an answer to inevitable questions about how to survive a full year without farming the land. The answer is very similar to what we saw with the manna, that in the sixth year, it would be multiplied so as to provide enough for the sixth day as well as the Sabbath. This is in addition to eating food from the land.
Before explaining some of the special cases in this chapter, I should point out a few things about the coming Israelite occupation of the promised land and the inheritance process. The promised land was given to Abraham as an inheritance, a possession which he would pass down to his children. When Jacob had his twelve sons, the land was divided amongst them with a double portion given to Joseph (i.e. a full portion given to both his sons Manasseh and Ephraim, equal to all other sons of Jacob). Practically, what that means is that the promised land is to be divided into thirteen portions (eleven sons plus two shares for Joseph).
But that's not the end of the story. The land must be divided amongst the people of each tribe, and in fact it follows the same pattern, with the firstborn of each son of Jacob getting a double portion and the rest of the sons getting a single portion. The land will continue being subdivided in this fashion as the population grows, leading to an obviously unsustainable situation with these familial inheritances shrinking with each generation. At first this isn't a problem because there's more land than Israelites to occupy it, but later this becomes a very real issue.
What's relevant to the Jubilee however is the notion of a perpetual inheritance. This notion underlies the very concept of the promised land, a land that is given to Abraham "forever" as an inheritance (Genesis 13:15). Similarly, each of the families in Israel is also supposed to have a perpetual inheritance, a small family plot that they can hold forever as their portion of the greater inheritance of Abraham. They share in the fate of their forebear.
The first special case is the distinction between city property and countryside property, with city property not reverting in the Jubilee, while open land and "houses of the villages... which have no surrounding walls" do revert in the Jubilee. I honestly do not understand why the author makes this distinction, except that the author is mainly thinking about land. With a house in a city, it is perhaps more of a physical possession (akin to clothing or tools) and not part of a person's "inheritance". That is, the perpetual inheritance I discuss above is more closely related to the land than any material possession. That's just my guess.
We are further told that the inheritance of the Levites is the houses in their cities. This is only explained later, but the Levites are not given a share of the land, their share is in cities. This is a direct consequence of Ex 32:29 and is explained in detail in the book of Numbers. Since we haven't read it yet, I will be brief and explain more fully in my commentary on Numbers, but the basic premise is that the tribe of Levi is about halfway between the "normal" tribes and the priesthood of Aaron. The Levites aren't quite priests, but they aren't quite laymen either. One of the many results of this is that the Levites are not given an inheritance of land, but rather they are given a number of cities and a small area of farmland surrounding those cities (the pasture fields of v. 34).
Next we are told that slaves are freed on the Jubilee. I believe this is in addition to the freedom that comes every seventh year (Ex 21:2). Slaves from other nations are not freed in the Jubilee, and may become permanent slaves. This is unusual considering how often we are told there is one law for foreigners and for Israelites. For instance, Ex 12:49, which states that foreigners may become circumcised, follow the laws of Moses, and enter the covenant by partaking in the Passover. There are several other references that basically insist that the Israelites not discriminate against the "stranger amongst you" because foreigners would be inherently vulnerable to discrimination. See e.g. Lev 19:34.
So this is one of the few distinctions between foreigners and Israelites in the law, and I believe what it comes down to is membership in the covenant. Remember that after the Passover in Ex 12, the LORD claimed ownership over the people of Israel, who agreed to a covenant of service to him. As v. 55 states, the sons of Israel are the LORD's servants, and as v. 23 states, the land belongs to the LORD. That's why the land cannot be permanently sold, because the Israelites are only tenants or hired servants of the LORD. Hence why the people cannot be permanently enslaved, because they already have a master.
I believe that when this chapter talks about "the pagan nations that are around you" and the "sons of the sojourners who live as aliens among you" that it is only talking about those foreigners who have not entered the covenant by circumcision.
Other than that, there's not much more to it. We have already seen some people sell themselves as hired servants (for instance, Jacob working for Laban) and it's not always a bad deal. Jacob actually came out pretty well from Laban, but then we can also see the negative side with Laban attempting to cheat Jacob out of his fair earnings. It is the intent of this chapter to protect against precisely those kinds of abuses, both by demanding fair treatment for hired servants and also by guaranteeing a termination to that service. This is consistent with the biblical idea of "perpetual inheritances" that I propounded above.
In practice, we will see many of these abuses practiced later in Israel's history, but in theory, they are all forbidden.