For there shall be a day, that the watchmen upon the mount Ephraim shall cry, Arise ye, and let us go up to Zion unto the LORD our God.
The watchmen ... shall cry. The watchmen, stationed on eminences (types of the preachers of the Gospel) shall summon the 10 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 Beersheba (Ezekiel 37:21-22).
Mount Ephraim - not one single mountain, but the whole mountainous region of the ten tribes.
Let us go up ... unto the Lord our God - from whom we formerly revolted, but who is now our God. A guarantee of that good time to come is given in the partial success of the Gospel in its first preaching in Samaria (Jeremiah 31:5; John 4:1; Acts 8:5-25).