Moses speaks to the Israelites as if they were one man, so except where noted the words "you" and "your" here are singular. (See: [[rc://en/ta/man/translate/figs-you]])
Possible meanings are 1) Moses is calling on all those who live in heaven and earth to be witnesses to what he says, or 2) Moses is speaking to heaven and earth as if they are people, and he is calling them to be witnesses to what he says (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-personification]] and [[rc://en/ta/man/translate/figs-apostrophe]])
Moses speaks to the Israelites as a group. (See: [[rc://en/ta/man/translate/figs-you]])
# obey his voice
Here "voice" refers to what Yahweh says. AT: "obey what he says" (See: [[rc://en/ta/man/translate/figs-metonymy]])
# to cling to him
"to rely on him"
# For he is your life and the length of your days
These phrases have the same meaning and are metonyms for Yahweh, emphasizing that he is the one who gives life and determines the length of people's lifetimes. AT: "Yahweh is the only one who can enable you to live a long life" (See: [[rc://en/ta/man/translate/figs-doublet]] and [[rc://en/ta/man/translate/figs-metonymy]])