Deuteronomy
Deuteronomy — the name means “second law” — is structured as one long farewell speech: Moses, at the very end of his life, addressing the generation that will enter the promised land he himself will never set foot in. He’s spoken to their parents’ generation before; this is essentially a re-teaching of the covenant for the people who will actually have to live it out.
Much of the book restates and expands law already given in Exodus and Leviticus, but with a different tone — less procedural, more exhortative, repeatedly urging the people to remember, to choose, to not forget what happened to their parents. The famous “Shema” (“Hear, O Israel: the Lord our God, the Lord is one”) and the command to love God with heart, soul, and strength both come from here, and Jesus later quotes this exact passage as the greatest commandment.
The book — and Moses’ life — ends with him viewing the promised land from a mountaintop, forbidden to cross into it himself because of an earlier act of disobedience, and dying within sight of it. Deuteronomy closes by noting that no prophet like him ever arose again in Israel — setting up an expectation the rest of the Old Testament keeps circling back to.