Albert Barnes Commentary Jeremiah 3:18

"In those days the house of Judah shall walk with the house of Israel, and they shall come together out of the land of the north to the land that I gave for an inheritance unto your fathers." — Jeremiah 3:18 (ASV)

With - To (margin). The prophet has just described the return of the ten tribes (Jeremiah 3:14 and following). Israel is represented as the first to repent, and Judah must go to her, so that they may return together to the Holy Land, no longer divided into Jews and Israelites, but merged into one people.

Out of the land of the north - The objection that the Jews were not carried like the Israelites into the northern provinces of Assyria (Jeremiah 3:12), but into Babylonia, misinterprets the whole prophecy. The gist of this is that if Israel repents, Judah must humbly seek her out and be content henceforth to take the inferior place, as having been the more guilty .