en_tn_condensed/jer/33/21.md

then you will be able to break my covenant with David ... and my covenant with the Levitical priests, my servants

This completes the sentence that began in verse 20 with the condition that is contrary to fact, "If you can break my covenant ... proper times." God said this to assure his people that no one can change God's covenants with David and the Levitical priests. This would give the people hope that God will keep his covenant. Alternate translation: "Just as you cannot break my covenant ... proper times, so you will never be able to break my covenant with David ... and my covenant with the Levitical priests, my servants" (See: rc://en/ta/man/jit/figs-hypo)

to reign 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/jit/figs-metonymy)