en_tn/deu/30/20.md

obey his voice

Here "voice" refers to what Yahweh says. Alternate translation: "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. Alternate translation: "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)

swore to your ancestors

The ellipsis can be filled in. Alternate translation: "swore that he would give to your ancestors" (See: rc://en/ta/man/translate/figs-ellipsis)