In this chapter, Moses restates the requirements of the Sabbath year.
This chapter is an expansion of Ex 21:2-11, which had previously established the terms of Hebrew slavery, freedom in the seventh year, and the provision for slaves who wish to remain with their master permanently (piercing the ear with an awl). The "year of remission" is structured very similarly to the Sabbath year, when the land rests and is not worked (Ex 23:10-11). We have not been specifically told that these two years (the Sabbath year and year of remission) were meant to coincide. We can reasonably infer that they coincide from the description of the Jubilee in Lev 25, however. In that chapter, the year of Jubilee occurs at the end of seven Sabbaths of years. The Sabbath year is when the land rests, but upon the Jubilee all land reverts to its historical ownership, essentially reverting the debt of those who have sold their land. This is very similar to the year of remission when slaves are "reverted" to their freedom and debts are released (v. 2).
I also think it's interesting to compare this to the seven years of service that Jacob offered for Leah and then Rachel. Jacob was freed in the seventh year, just like slaves are freed in the seventh year. I'm not sure if we're meant to connect these two things, but it's interesting to think about.
Anyway, the discussion here is far longer and more detailed than Ex 21. This chapter teaches that not only are Hebrew slaves to be freed, but other debts are also released and anything loaned to a neighbor is given to that neighbor without repayment. Furthermore, upon freeing a slave the owner is expected to give that person gifts. All of these are related points, and the general idea is to give the poor a renewed opportunity and to prevent the formation of a perpetual underclass. While people in Israel might drift down into poverty for whatever reason, their fellow countrymen are prohibited from exploiting the poor and drawing them into a perpetual slavery. Because the LORD freed the Israelites from slavery in Egypt, he prohibits the Israelites from permanently enslaving one another.
I think there's an amusing interplay between the expectation that "the poor will never cease to be in the land" (v. 11) and "the LORD will surely bless you". In fact, v. 4 says "there will be no poor among you", while later in the same chapter we are told there would always be poor people in the land. The covenant is full of aspirational language related to the blessings of the LORD, but the practical reality is that ancient Israelite did have poor people. One important factor is that the Israelites never really followed the covenant and later in the OT they will be frequently rebuked for (among other things) not freeing slaves in the Sabbath year. It is peculiar that the covenant contains provisions (like how to treat poor people) that seem to assume the nation will not follow the covenant. I'm not really sure how to explain this discrepancy, and in such a short range of text.
I would also like to point out that the Sabbath year corresponds with the fourth commandment, to honor the Sabbath day. This chapter can be viewed as an expansion of the Sabbath day principle, which is about honoring the LORD, taking a day of rest and focusing upon the LORD. The idea of "rest" is apparently expanded to include freedom and remission of debt, probably by equating debt with burdens. So the Sabbath year is meant to give the Israelites "rest" from their debt.
The chapter concludes by reminding us that the Israelites are to slaughter their firstborn animals every year before the temple, but only if those animals have no defects. Ex 13 didn't tell us this, but there are many passages that say offerings to the LORD must have no defects (Lev 1:3, 3:6, 4:3, 9:2, 14:10, 22:19, and many more), so I am not surprised. Defective animals are to be eaten "within your gates", so they are not allowed to live, but must not be brought before the LORD.