As no one can break Jehovah's covenant with respect to the day and His covenant with respect to the night, so that day and night will not be at the appointed time, so His covenant with David His servant can never be broken, so that he will not have a son to reign on his throne. Likewise, His covenant can never be broken with the Levitical priests as His ministers (vv. 17-21).
Verse 22 says that as the host of heaven cannot be numbered and the sand of the sea cannot be measured, so Jehovah will multiply the seed of David His servant and the Levites His ministers.
If Jehovah's covenant with respect to day and night does not stand, if He has not established the statutes of heaven and earth, then He will also reject the seed of Jacob and David His servant and will not take rulers from his seed to be over the seed of Abraham, Isaac, and Jacob; for He will turn their captivity and have compassion on them (vv. 23-26; 31:35-36). Here God is assuring His people that just as the universe remains forever, so the people of God and the royal family will also remain forever.