en_tn/psa/089/029.md

his throne as enduring as the skies above

Someone from David's family always ruling as king is spoken of as if his his throne would last as long as the sky will last. (See: rc://en/ta/man/translate/figs-simile)

his throne

Here "throne" represents the power to rule as king. (See: rc://en/ta/man/translate/figs-metonymy)