John Gill Commentary Jeremiah 31:1

"At that time, saith Jehovah, will I be the God of all the families of Israel, and they shall be my people." — Jeremiah 31:1 (ASV)

At the same time, says the Lord. The time of the Messiah, the Gospel dispensation, the latter days; when the Jews shall consider the prophecies of the Old Testament, and observe how they have been fulfilled in Jesus; and shall reflect upon their disbelief and rejection of him; and shall turn unto him, and serve the Lord their God, and David their king; see (Jeremiah 30:9Jeremiah 30:21Jeremiah 30:22Jeremiah 30:24).

will I be the God of all the families of Israel; not of some few persons only, or of one of a city, and two of a family, but of every family; and this will be when "all Israel" shall be converted and saved, and a nation shall be born at once; then will God show himself to them as their covenant God, manifest his love to them, and bestow the blessings of his grace upon them:

and they shall be my people; behave as such to him; own him to be their God, and serve and worship him.