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

"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" This completes the sentence that began in verse 20. God said this to assure his people that no one can change God's covenants, giving the people hope.  

# to reign on his throne

"to rule the kingdom I have given to him"