Commentaries
4:1,2 The first two verses should be read with the last chapter. Sin must be put away out of the heart, else it is not put away out of God's sight, for the heart is open before him.
2. And thou—rather, "And if (carried on from Jer 4:1) thou shalt swear, 'Jehovah liveth,' in truth, &c.", that is, if thou shalt worship Him (for we swear by the God whom we worship; compare De 6:13; 10:20; Isa 19:18; Am 8:14) in sincerity, &c.
and the nations—Rather, this is apodosis to the "if"; then shall the nations bless themselves in (by) Him" (Isa 65:16). The conversion of the nations will be the consequence of Israel's conversion (Ps 102:13, 15; Ro 11:12, 15).