RobH_en_tn/jer/33/21.md

then you will be able to break my covenant with David my servant

The hypothetical statement that begins with the words "If you can break my covenant ... times," in verse 20 ends here. No one can change day and night, and no one can change God's covenant with David. Alternate translation: "You know that you cannot break my covenant ...times, so you know that you will never be able to break my covenant with David my servant" (See: rc://en/ta/man/translate/figs-hypo)

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)