en_tn/deu/30/19.md

I call heaven and earth to witness

Possible meanings are 1) Moses is calling on all those who dwell 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)

obey his voice

AT: "obey what he says" (See: rc://en/ta/man/translate/figs-metonymy)

and to cling to him

"and to rely on him"

For he is your life and the length of your days

This means that Yahweh is the one who can give the Israelites a long life.