Return, ye backsliding children, etc.; more literally, Turn, ye turned-away sons; I will heal your turnings (as Hosea 14:4). It seems strange at first sight that this verso does not stand before Jeremiah 3:21.
But the truth is that Jeremiah 3:21 describes not so much the "conversion" of the Jews as their willingness to "convert", or "turn" to God. Christ must touch, or at least make his presence felt, in order that the sick man may be healed; a special call of God must be heard, in order that the sinner may truly repent.
Behold, we come unto thee. Efficacious, and not "irresistible" grace, is the doctrine of the Old Testament.