Jeremiah 3:6

The very wording of the passage that has been read has something obscure in it, which must first be understood; and after this, if God grants it, we shall come to know his mystical intent. Now he wants us to know this: that, as is written in the books of Kingdoms, the people were divided in the times of Rehoboam into the kingdom of the ten tribes under Jeroboam and into that of the two tribes under Rehoboam; and those under Jeroboam were called Israel, but those under Rehoboam Judah. And this division of the people has remained, so far as concerns the historical record, down to the present; for we know of no historical account that has gathered Israel and Judah together into one. Now Israel sinned first and more grievously — the people under Jeroboam and his successors — and sinned so much beyond Judah that they were condemned by Providence to become captives "into Assyria," as the Scripture says, "unto this day." After this the sons of Judah also sinned and were condemned to captivity into Babylon, not "unto this day" as Israel, but for "seventy years," concerning which Jeremiah prophesied, and which Daniel also mentioned. If we understand these things as spoken with reference to that people of that time, look at the words of the prophet, whether they do not indicate something of this sort. For he accuses, as it were, the sins of Israel, and says that, when so many sins had been committed by Israel, the congregation of Judah, having heard of their transgressions and in what manner I made them come to be in captivity, was not instructed but added to its sins, so that, because of this addition of sins when compared with the sins of Israel, righteousness was found in Israel over against Judah. Then, upon these things, the prophet is commanded to prophesy, since Judah had become worse than Israel, in order that after its sins it might turn back. […]

Those who place themselves far from your care and choose to serve idols will reap the destructive fruit of defection. He calls idolatry infidelity here. God likewise says also through Jeremiah, "She went up every high hill and under every green tree and was unfaithful …

It is written in the law: "You shall not commit adultery." This is rightly observed according to the simple meaning of the letter by one who is still in bondage to foul passions. But by one who has already forsaken these dirty acts and impure affections, it must be observed in the spirit, so that he may forsake not only the worship of idols but also all heathen superstitions and the observance of auguries and omens and all signs and days and times, or at any rate he should not be entangled in the conjectures of words and names that destroy the simplicity of our faith. This is the kind of fornication by which Jerusalem is said to have been corrupted, the fornication "on every high hill and beneath every leafing tree." The Lord criticized Jerusalem for this through the words of the prophet, "Let them stand and save you, these astrologers who studied the stars and counted the months so as to tell from these what was coming to you."

(Verse 6 and following) And the Lord said to me in the days of King Josiah: Have you seen what the adulteress Israel has done? She went upon every high hill and under every leafy tree and committed adultery there. And I said, after she had done all these things: Return to me, but she did not return. And her treacherous sister Judah saw that I had dismissed the adulteress Israel and had given her a bill of divorce. But her treacherous sister Judah did not fear, but she also went and committed adultery.

If, then, he says that first I sent away Israel because of its sins and sent it into deportation, but Judah, hearing what had happened to Israel, did not turn back, he speaks concerning our own sins. Since the things that befell Israel are read, and the transgressions concerning that people, we ought to fear, and: "if he did not spare the natural branches, how much more will he not spare us either; if that One who is both kind and at the same time loving to mankind, God, did not spare but cut off those who boasted to be a 'cultivated olive tree,' those rooted in 'the root' of the patriarchs Abraham and Isaac and Jacob, how much more will he not spare us." For he is not kind and yet not severe, nor severe and yet not kind. For if he were only kind but not severe, we would to a greater degree despise "his kindness." If he were severe but not kind, perhaps we would even despair over our sins. […]