Charles Spurgeon Commentary Jeremiah 33:23-26

"And the word of Jehovah came to Jeremiah, saying, Considerest thou not what this people have spoken, saying, The two families which Jehovah did choose, he hath cast them off? thus do they despise my people, that they should be no more a nation before them. Thus saith Jehovah: If my covenant of day and night [stand] not, if I have not appointed the ordinances of heaven and earth; then will I also cast away the seed of Jacob, and of David my servant, so that I will not take of his seed to be rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and will have mercy on them." — Jeremiah 33:23-26 (ASV)

This will be literally fulfilled in the latter days, I do not doubt, but it is even now being fulfilled to the spiritual seed of Jacob and David. The covenant of grace is made sure to all the seed, even to as many as have believed in Christ's name.