“All The Commandment” | Why in the Singular

“You shall faithfully observe all the Instruction (Heb. kol ha-mitzvah) that I enjoin upon you today, that you may thrive and increase and be able to possess the land that the Lord promised on oath to your fathers” (Deut. 8:1).

The beginning of this verse presents a linguistic difficulty: why does it say kol ha-mitzvah in the singular, not kol ha-mitzvot (= “all the commandments”) in the plural, as would be quite reasonable given the context? How are we to understand the plain sense of the verse? Did the Torah use the singular to indicate just one commandment, or perhaps a single specific commandment? Or are we to see this “instruction” as subsuming the entire body of commandments as one?