The Scofield Bible Commentary, by Cyrus Ingerson Scofield, , at sacred-texts.com
The Lord said
The general character of the second message to Judah is:
(1) of reproach that the example of Jehovah's chastening of the northern kingdom (Kg2 17:1-18) had produced no effect upon Judah, for example (Jer 3:6-10).
(2) of warning of a like chastisement impending over Judah, for example (Jer 3:15-17).
(3) of touching appeals to return to Jehovah, for example (Jer 3:12-14).
(4) of promises of final national restoration and blessing, for example (Jer 3:16-18).
"Israel" and "Ephraim": names by which the northern kingdom (the ten tribes) is usually called in the prophets. When by "Israel" the whole nation is meant, it will appear from the context.