We now see more clearly for what purpose Jeremiah compared the ten tribes with the kingdom of Judah; it was done in order to shew that the Jews, who wished to be deemed far more holy than others, were yet more perfidious and deserved a heavier punishment, because they acted so deceitfully with God. It may be here asked, why he pronounces the Jews worse than the Israelites, while they still continued in a sort of middle state of things. We indeed know that the kingdom of Judah was become so corrupt, that hardly any religion remained there; yet the temple was still standing and the priesthood still existed at Jerusalem. But the Prophet condemns the Jews more than the Israelites for other reasons, even because they ought to have become wise through the calamities of others, and they ought to have been confirmed in true religion when they saw their brethren falling away from the pure worship of God: these things they ought to have maturely considered. It was this supine sottishness that rendered them worse than all their brethren, and also their pride, the chief cause of their condemnation, for they boasted that they remained perfect, while the ten tribes had become degenerated. These were the reasons why he says that Israel, though a perfidious woman, was yet more righteous than her sister Judah. The language indeed is not to be strictly taken when it is said, that she justified her soul; for God does not here excuse the Israelites, nor does he free or absolve them from guilt, (for he had severely punished them;) but this way of speaking is commonly used by the prophets; -- Sodom was righteous in comparison with Jerusalem; and Tyre and Sidon were just when compared with the Jews. (Ezekiel 16:47, 48.) Justified then has she her soul, [1] even the treacherous or the apostate Israel, in comparison with the perfidious Judah; that is, for the reasons which I have stated. The obstinacy of the Jews was greater and less excusable: the external worship of God, which they had retained, ought to have been a bridle to check them; and they had also seen how severe a judge God had been towards the ten tribes; but the judgments of God they despised, and derived no benefit from them.

Footnotes

1 - This is the literal expression, but the word nphs is often taken for oneself, and ought often to be so rendered. See Numbers 30:5; Job 18:4; Psalm 7:2; God is said to swear by his soul, that is, by himself, Amos 6:8 -- Then said Jehovah to me, -- Justified herself hath apostate Israel, More than the hypocrite Judah. Manifest and open apostasy is more honest than the double dealing of hypocrites, who combine God's worship with idolatry; nor is it so hateful to God. -- Ed.

Hath justified herself - Judah had had the benefit of the warning given by Israel's example. Both abandon Yahweh's service for idolatry, but Israel is simply "apostate," Judah is also false.
The verse is important,
(1) as accounting for the destruction of Jerusalem so soon after the pious reign of Josiah. Manasseh's crimes had defiled the land, but it was by rejecting the reforms of Josiah that the people finally profaned it, and sealed their doom:
(2) As showing that it is not by the acts of its government that a nation stands or falls. Ahaz and Manasseh lent the weight of their influence to the cause of idolatry: Hezekiah and Josiah to the cause of truth. But the nation had to determine which should prevail. Excepting a remnant it embraced idolatry, and brought upon itself ruin: in the remnant the nation again revived Jeremiah 24:5, Jeremiah 24:7.

Backsliding Israel hath justified herself more - She was less offensive in my eyes, and more excusable, than treacherous Judah. So it is said, Luke 18:14, the humbled publican went down to his house justified rather than the boasting Pharisee. The one was more to be pitied than the other, and more likely to receive the mercy of God.

And the LORD said to me, The backsliding Israel hath (n) justified herself more than treacherous Judah.
(n) Israel has not declared herself as wicked as Judah, who yet has had more admonitions and examples to call her to repentance.

And the Lord said unto me,.... To the Prophet Jeremiah, as in Jeremiah 3:6 and at or about the same time:
the backsliding Israel hath justified herself more than treacherous Judah; that is, was comparatively more righteous; of the two she appeared the most righteous; though neither of them could vindicate their conduct, or justify themselves before God; see Luke 18:14. Judah was most to blame, because that after Israel committed idolatry, and was carried captive, she took no warning by it, but fell into the same sin; and in Manasseh's time committed greater idolatries, and more wickedness, than ever Israel did; and more than even the Amorites themselves, and other Heathen nations, had done, 2-Kings 21:6 and though a reformation was made in Josiah's time, it was only feignedly, it was not cordial and hearty; and therefore she is all along here charged with perfidy and treachery.

justified herself--has been made to appear almost just (that is, comparatively innocent) by the surpassing guilt of Judah, who adds hypocrisy and treachery to her sin; and who had the example of Israel to warn her, but in vain (compare Ezekiel 16:51; Ezekiel 23:11).
more than--in comparison with.

Israel's return, pardon, and blessedness. - Jeremiah 3:11. "And Jahveh said to me, The backsliding one, Israel, is justified more than the faithless one, Judah. Jeremiah 3:12. Go and proclaim these words towards the north, and say, Turn, thou backsliding one, Israel, saith Jahveh; I will not look darkly on you, for I am gracious, saith Jahveh; I will not always be wrathful. Jeremiah 3:13. Only acknowledge thy guilt, for from Jahveh thy God art thou fallen away, and hither and thither hast thou wandered to strangers under every green tree, but to my voice ye have not hearkened, saith Jahveh. Jeremiah 3:14. Return, backsliding sons, saith Jahveh; for I have wedded you to me, and will take you, one out of a city and two out of a race, and will bring you to Zion; Jeremiah 3:15. And will give you shepherds according to my heart, and they will feed you with knowledge ad wisdom. Jeremiah 3:16. And it comes to pass, when ye increase and are fruitful in the land, in those days, saith Jahveh, they will no more say, 'The ark of the covenant of Jahveh;' and it will no more come to mind, and ye will not longer remember it or miss it, and it shall not be made again. Jeremiah 3:17. In that time they shall call Jerusalem the throne of Jahveh; and to it all peoples shall gather themselves, because the name of Jahveh is at Jerusalem: and no longer shall they walk after the stubbornness of their evil heart. Jeremiah 3:18. In those days shall the house of Judah go along with the house of Israel, and together out of the land of midnight shall they come into the land which I have given for an inheritance unto your fathers." In Jeremiah 3:11, from the comparison of the faithless Judah with the backsliding Israel, is drawn the conclusion: Israel stands forth more righteous than Judah. The same is said in other words by Ezekiel 16:51.; cf. (Ezek.) Jeremiah 23:11. צדק in Piel is to show to be righteous, to justify. נפשׁהּ, her soul, i.e., herself. Israel appears more righteous than Judah, not because the apostasy and idolatry of the Israelites was less than that of the people of Judah; in this they are put on the same footing in Jeremiah 3:6-10; in the like fashion both have played the harlot, i.e., stained themselves with idolatry (while by a rhetorical amplification the apostasy of Judah is in Jeremiah 3:9 represented as not greater than that of Israel). But it is inasmuch as, in the first place, Judah had the warning example of Israel before its eyes, but would not be persuaded to repentance by Israel's punishment; then again, Judah had more notable pledges than the ten tribes of divine grace, especially in the temple with its divinely-ordained cultus, in the Levitical priesthood, and in its race of kings chosen by God. Hence its fall into idolatry called more loudly for punishment than did that of the ten tribes; for these, after their disruption from Judah and the Davidic dynasty, had neither a lawful cultus, lawful priests, nor a divinely-ordained kingship. If, then, in spite of these privileges, Judah sank as far into idolatry as Israel, its offence was greater and more grievous than that of the ten tribes; and it was surely yet more deserving of punishment than Israel, if it was resolved neither to be brought to reflection nor moved to repentance from its evil ways by the judgment that had fallen upon Israel, and if, on the contrary, it returned to God only outwardly and took the opus operatum of the temple-service for genuine conversion. For "the measure of guilt is proportioned to the measure of grace." Yet will not the Lord utterly cast off His people, Jeremiah 3:12. He summons to repentance the Israelites who had now long been living in exile; and to them, the backsliding sons, who confess their sin and return to Him, He offers restoration to the full favours of the covenant and to rich blessings, and this in order to humble Judah and to provoke it to jealousy. The call to repentance which the prophet is in Jeremiah 3:12 to proclaim towards the region of midnight, concerns the ten tribes living in Assyrian exile. צפנה, towards midnight, i.e., into the northern provinces of the Assyrian empire the tribes had been carried away (2-Kings 17:6; 2-Kings 18:11). שׁוּבה, return, sc. to thy God. Notwithstanding that the subject which follows, משׁבה, is fem., we have the masculine form here used ad sensum, because the faithless Israel is the people of the ten tribes. לא אפּיל פּני, I will not lower my countenance, is explained by Genesis 4:5; Job 29:24, and means to look darkly, frowningly, as outward expression of anger; and this without our needing to take פּני for כּעסי as Kimchi does. For I am חסיד, gracious; cf. Exodus 34:6. As to אטּור, see on Jeremiah 3:5.