The prophet shows that the happiness of Israel and Judah, united in one prosperous nation, will rest upon the consciousness that their chastisement has been the result of sins which they have themselves committed, and that God‘s covenant depends not upon external sanctions, but upon a renewed heart.
Jeremiah 31:27
So rapid shall be the increase that it shall seem as if children and young cattle sprang up out of the ground.
Jeremiah 31:29, Jeremiah 31:30
A sour grape - Better, sour grapes. The idea that Jeremiah and Ezekiel (marginal reference) modified the terms of the second Commandment arises from a mistaken exegesis of their words. Compare Jeremiah 32:18; Deuteronomy 24:16. The obdurate Jews made it a reproach to the divine justice that the nation was to be sorely visited for Manasseh‘s sin. But this was only because generation after generation had, instead of repenting, repeated the sins of that evil time, and even in a worse form. justice must at length have its course. The acknowledgment that each man died for his own iniquity was a sign of their return to a more just and right state of feeling.
Jeremiah 31:31
A time is foretold which shall be to the nation as marked an epoch as was the Exodus. God at Sinai made a covenant with His people, of which the sanctions were material, or (where spiritual) materially understood. Necessarily therefore the Mosaic Church was temporary, but the sanctions of Jeremiah‘s Church are spiritual - written in the heart - and therefore it must take the place of the former covenant Hebrews 8:13, and must last forever. The prophecy was fulfilled when those Jews who accepted Jesus of Nazareth as the Messiah, expanded the Jewish into the Christian Church.
Jeremiah 31:32
Although - i. e., although as their husband (or, “lord” (Baal, compare Hosea 2:16)) I had lawful authority over them. The translation in Hebrews 8:9 agrees with the Septuagint here, but the balance of authority is in favor of the King James Version.
Jeremiah 31:33
The old law could be broken Jeremiah 31:32; to remedy this God gives, not a new law, but a new power to the old law. It used to be a mere code of morals, external to man, and obeyed as a duty. In Christianity, it becomes an inner force, shaping man‘s character from within.
Jeremiah 31:34
I will forgive their iniquity - The foundation of the new covenant is the free forgiveness of sins (compare Matthew 1:21). It is the sense of this full unmerited love which so affects the heart as to make obedience henceforward an inner necessity.