The reunion of the separated portions of the nation (comp. Ezekiel 37:16, Ezekiel 37:17; Hosea 1:11; Isaiah 11:12, Isaiah 11:13). Observe, Israel is converted first, then Judah. This detail in the prophecy is not to be pressed.
Not that the force of any prophecy is to be evaded, but that in this case the form of the statement is so clearly conditioned by the abounding sympathy of the prophet for the ten tribes. These had been so long languishing in captivity that they needed a special premise.
The form of the promise is imaginative; this seems clearly to follow from the fact that in no other passage (except, indeed, Jeremiah 31:9) is there a reference to the spiritual primacy of Etihraim in the restored nation.
Out of the land of the north; i.e. Assyria and (Jeremiah 1:14) Babylonia. The Septuagint inserts, "and from all the countries," agreeably to Jeremiah 16:15; Jeremiah 23:3; Jeremiah 32:37. Of course, it would not be an accurate statement that the exiles from Judah were confined to "the land of the north."
This is a fair specimen of the supplementing tendency of the Septuagint, though it is possible, and even probable, that the Hebrew text has suffered in a less degree from the same tendency on the part of later copyists.