en_tn/jer/33/21.md

my covenant with day and night ... my covenant with David my servant

No one can change day and night, and no one can change God's covenant with David.

to sit on his throne

The throne is a metonym for the king who sits on the throne. Alternate translation: "to rule the kingdom I have given to him" (See: rc://en/ta/man/translate/figs-metonymy)