en_tn/psa/089/004.md

I will establish your descendants forever

Yahweh always causing one of David's descendants to be king is spoken of as if David's descendants are a building that Yahweh will build and make firm. (See: rc://en/ta/man/translate/figs-metaphor)

I will establish your throne through all generations

Here "throne" represents the power to rule as king. The psalmist speaks of God promising that one of David's descendants will always rule as king as if God will build David's throne and make it firm. AT: "I will make sure that one of your descendants will rule as king over every generation of my people" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-metaphor)