Jeremiah 33:26
Then will I cast away the seed of Jacob, and David my servant, so that I will not take any of his seed to be rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and have mercy on them. Then will I cast away the seed of Jacob, and David my servant, so that I will not take any of his seed to be rulers over the seed of Abraham, Isaac, and Jacob: for I will cause their captivity to return, and have mercy on them.
Jeremiah 33 stands late in Jeremiah's work in Judah, after chapter 37 and before chapter 38. It promises that God will not cast away the seed of Jacob nor abandon His promise that David's seed will be rulers over the seed of Abraham, Isaac, and Jacob, for He will cause their captivity to return and have mercy on them. It belongs to the Messianic prophecies that look through the restoration from Babylon to the more glorious restoration under Christ Jesus our Lord, accomplished through Jesus.
The Israel to be preserved and restored is all who are counted as Abraham's seed by faith, all the children of promise counted as Israel, not merely the natural descendants living at a particular time nor indiscriminately those who reject the covenant. The faithful remnant of literal Israel was a type of Israel under the new covenant. The promised gathering and deliverance is fulfilled when God gathers His people, gives them His Spirit, and brings them into the promised land.
That gathering takes place just before the resurrection of the righteous and includes living saints from every nation as well as many literal Israelites, and the promised restoration includes the resurrection at the second coming. During the thousand years the earth will be desolate after all wicked men are destroyed at the second advent, while the righteous dead raised and the living righteous changed to immortality ascend with Christ to the eternal city and reign with Him in the judgment of the wicked. In that restored kingdom the children of promise retain their personal and national identity and Israel receives the promises made to it, and those who were Levites will serve in the heavenly Jerusalem, the heavenly country.