The Covenant is not merely for those who were there with Moses on that day, but for all of their descendants, leading up to the present time. There is an interpretation of this that says that each of us is there at that moment as well as being where we currently are. We are in suspension there, and that suspension informs us where we are now.
Interestingly, Moses predicts that the whole enterprise of occupying Canaan will fail, that the Children of Israel will be exiled after being conquered and subjugated by foreign armies, after significant moral collapse. He predicts that in exile, the Israelites will repent, and be allowed to return. In the Documentary Hypothesis, the Deuteronomist is writing during the time of the Babylonian exile, which gives these words a sense of hope rather than the defeatism that they would have if they were written in Moab on the West Bank of the Jordan, before the conquest of Canaan began.
Moses warns that, before the exile will be lifted, God will circumcise the foreskins of the hearts of the people who seek to return. The toughness around their hearts will be pared away, leaving a heart that is raw and tender. Only those with tender hearts can have the right attitude towards God and His commandments. Our society places a lot of value on being cool, but being emotionally aloof is a form of weakness. One has to have the heart open and raw and tender in order to perceive the emotional content in reality. Many rationalists are afraid of their emotions, mostly because they are afraid of being overpowered by their emotions. Moses is not advocating that our emotions overwhelm our reason, but that our experiences have non-negligible emotional content.
In Masonry, we say that the Compasses are a tool for circumscribing our desires and keeping our passions within due bounds. Every experienced Mason at least once has heard a WM flub his line and say "circumcising our desires", and it's usually good for a chuckle. But Moses is warning us that God will do precisely that. He will circumcise our hearts, the seat of our desires. Again, Masonry shows where this is going, and how to handle this the right way. We should not repress our desires, but merely to draw a circle and keep our desires within that circle, keeping our passions within due bounds. To the 18th century mind, passion was not a complimentary word. If you read the acid way in which George Washington talked about enthusiasm, you will see that these bursts of emotion made those in the Enlightenment Era very uncomfortable. And yet a person devoid of emotion is not human. By drawing boundaries, we allow for an emotional life that doesn't overwhelm our rational life.
The next passage is often quoted, but is more often completely forgotten:
For this commandment which I command thee this day, it is not hidden from thee, neither is it far off. It is not in heaven, that thou shouldest say, Who shall go up for us to heaven, and bring it unto us, that we may hear it, and do it? Neither is it beyond the sea, that thou shouldest say, Who shall go over the sea for us, and bring it unto us, that we may hear it, and do it? But the word is very nigh unto thee, in thy mouth, and in thy heart, that thou mayest do it. [Deuteronomy 30: 11-14].Everyone has access to the Torah. It is immediate. We carry it in our mouths and in our hearts. This is the Jewish version of "if you meet the Buddha on the road, kill him." But it is a lesson that people continually fail to learn. No human can intercede with God on your behalf. There is no need to travel to a faraway country to find God. God is right here, right now.