en_tn/psa/119/111.md

I claim your covenant decrees as my heritage forever

The writer always cherishing and obeying God's decrees is spoken of as if the decrees are land or a possession that the writer will inherit. AT: "Your laws will belong to me forever" or "Your covenant decrees are like a heritage I will keep forever" (See: rc://en/ta/man/translate/figs-metaphor)

they are the joy of my heart

Here "heart" represents the whole person. AT: "they make me joyful" or "I delight in them" (See: rc://en/ta/man/translate/figs-synecdoche)

My heart is set on obeying

Here "heart" represents the writer's will. The phrase "heart is set" is an idiom. It is a way of saying the writer is determined. AT: "I am determined to obey" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-idiom)

to the very end

Possible meanings are 1) "every one of them" 2) "to the very end of my life" or 3) "to the very end of time"