Moses continues to speak to the people of Israel if they were one man, so all instances of "you" and "your" are singular. (See: [[rc://en/ta/man/jit/figs-you]])
The two phrases "in heaven" and "on the earth" show two extremes and mean "everywhere." Alternate translation: "over everything" (See: [[rc://en/ta/man/jit/figs-merism]])