Jamieson, Fausset and Brown on Jeremiah 31:6

6. The watchmen stationed on eminences (types of the preachers of the gospel), shall summon the ten tribes to go up to the annual feasts at Jerusalem ("Zion"), as they used to do before the revolt and the setting up of the idol calves at Dan and Beer-sheba (Eze 37:21, 22).

Mount Ephraim--not one single mountain, but the whole mountainous region of the ten tribes.

our God--from whom we formerly revolted, but who is now our God. An earnest of that good time to come is given in the partial success of the gospel in its first preaching in Samaria (Joh 4:1-42; Ac 8:5-25).