This chapter begins the specific stipulations (with the prior chapter listing the general stipulations). That is, the ten commandments build a framework of sorts, which the rest of Deuteronomy is now filling in. This chapter in particular corresponds with the first commandment, to have no other gods before the LORD. The general principle is that the LORD must be foremost in one's life.
Of course, we could say that the entire Pentateuch relates to the first commandment, because devotion to the LORD is central to the covenant as a whole. In fact, when Jesus is asked what is the greatest commandment, he quotes Deut 6:5, that you must love the LORD with all your heart and soul and strength (Matthew 22:37, Mark 12:30, Luke 10:27 has a slight variation). Mark also quotes v. 4 in addition to v. 5. It is therefore a pivotal verse to Christianity, because loving God is what defines the "commandments".
In the context of the covenant, the commandments are an expression of our obligation to the LORD. The ten commandments are a list of things that the holders of the covenant are expected to do. The "greatest commandment" therefore embodies that obligation, and what it comes down to is singular, devoted love to the LORD. What the LORD gives us in return is partially explained by v. 21-23, that the LORD brought the Israelites out of slavery and into the land that had been promised, a rich land "flowing with milk and honey".
Verse 4 is called the "Shema", (which is Hebrew for "hear" or "listen") and it is one of the central prayers of Judaism, recited on many occasions. The Shema takes the implicit monotheism of the first commandment (to have no other gods besides the LORD) and makes it explicit: there are no other gods besides the LORD. Translations of the Shema have varied, but the basic Hebrew says something like this: "Listen Israel, LORD God LORD one". As my readers have probably noticed, the Hebrew is lacking in verbs, so we have to fill in the blanks to figure out exactly how to construct this into a sentence. Most translations turn this into two phrases, "the LORD is God, the LORD is one" because the repetition of the word LORD suggests that this is a parallel construction (i.e. equating "God" with "one" as descriptors of the LORD).
The Jewish version replaces the divine name with "Adonai", the Hebrew for "lord", out of a desire to observe the third commandment (you shall not bear the name of the LORD "falsely", traditionally "in vain"). I can hardly think of a more appropriate use of the divine name than repeating it in the Shema, so obviously this is a point on which I disagree with the traditional Jewish approach. I have also used the divine name on numerous occasions within this commentary, which I also think is appropriate because it seems foolish to me to study the bible and refuse to speak of God by name.
The (orthodox) Jewish tradition is to maintain a literal adherence to all of the commandments as conservatively as possible. One example that really brings this out is v. 7-9:
You shall teach them diligently to your sons and talk of them ... when you lie down and when you rise up. You shall bind them as a sign on your hand and they shall as frontals on your forehead. You shall write them on the doorposts of your house and on your gates.The way that I understand these verses, Moses is commanding the Israelites to always keep these commandments foremost in their actions (sign on your hand) and thoughts (frontals on your forehead). The Israelites are to speak of them to others and contemplate upon them continually, both in the outside and within their homes. To me, these verses appear to be figurative, both because the language seems figurative and because it is in the larger context of Deuteronomy. Deuteronomy is Moses's last, grand speech. I think it's safe to say that Moses is trying to put everything in the strongest terms possible. With all of these factors put together, I think verses 7-9 are supposed to deeply encourage us to consider the commandments of the LORD in all circumstances of life, everywhere and with everyone.
To the orthodox Jewish tradition, however, these verses have been expanded into a literal understanding. What they did is take small scrolls with the Shema and maybe other verses and put them into small boxes (called tefillin), and then attached those boxes to their clothing near the head and hand. Then they put similar boxes upon the doorframes of their houses (these boxes are called mezuzah). Another tradition is to recite the Shema when going to sleep and arising in the morning. And thus, the Jews have sought (and still seek) to literally fulfill v. 7-9 as if they were intended literally.
There's no better explanation for this behavior than v. 25: "It will be righteousness for us if we are careful to observe all this commandment before the LORD our God". The word "righteousness" here is the same word that was used in Gen 15:6, when Abraham "believed in the LORD, and it was counted to him as righteousness". Abraham was righteous by faith, the Israelites are righteous by observance of the law. It should come as little surprise that the Israelites and their descendants would make that observance as carefully as possible.
Verses 7-9 are really just a microcosm of the orthodox approach to the whole OT. We see another example in what I discussed above concerning the divine name; Jews refuse to mention the divine name, YHWH, or sometimes even the word God, because it's impossible to "bear the name falsely" if one does not "bear the name" at all. It's unfortunate collateral damage if the divine name is most frequently used in the scriptures and prayer, so the name of God is most thoroughly stripped from the subjects that relate to God. Similarly, the correct pronunciation of YHWH has been lost because Jewish tradition prohibits speaking the name and also because the biblical text lacks vowel markings. While this wasn't entirely the intent of the Israelites, it was the effect.
A third example is Ex 23:19, you shall not boil a goat in its mother's milk. To maintain observance of this commandment in all possible circumstances, the Jewish tradition changed this law to "you shall not eat meat and dairy in the same meal", which is a much broader requirement. In my commentary on Ex 23, I called this "building a fence around the Torah", meaning that the requirements of the Torah are defensively buffered with additional requirements. What we see in v. 25 here is the reason why they build a fence around the Torah: it is their righteousness to observe the law, so every ambiguity is interpreted as broadly as possible to avoid offending the law.
The Christian approach is generally a lot closer to the righteousness of Abraham, emphasizing faith in God and loving the LORD (v. 5). We must wait until the NT before I can discuss the Christian tradition in depth, but I want my readers to understand the context being laid out here and how it relates to both the Jewish and Christian faiths. Christianity represents a significant deviation from historical Judaism. This chapter helps us understand historical Judaism, and once we reach the NT I hope to explain the reasons for the significant deviation.