Additional note on the interpretation of the new covenant.

The plain sense of the prophecy in 31:31-34 relates it to the historical nations of Israel and Judah. It refers, in the first place, to the return of exiles from Babylon. This is clear from the reference to the rebuilding of the city in vs 38-40. The whole tendency of chs. 30-31 has been in this direction also. The new covenant prophecy, therefore, has a first fulfilment when God brings back the exiles in 539 BC and the following years.
However, the prophecy suggests more than this. The inclusion of ‘Israel’, which had ceased to exist as a nation by Jeremiah’s time, suggests that a deeper fulfilment is looked for than a mere physical return to the land. The ancient covenant is to be fulfilled at last in a new way, by a people that is capable of entering into it, by God’s help.
The NT teaches that the decisive fulfilment of the new covenant prophecy takes place in Jesus Christ (1 Cor. 11:25; Heb. 8:7-13; 9:15). This means that God’s covenant is finally achieved in the people who are ‘in Christ’. The new kind of forgiveness is possible because he has made a once–for–all sacrifice for sin that makes all other sacrifices obsolete (Heb. 10:15-18). It is a covenant that cannot end because it has been perfected by Christ. Even so, his new people are called to faithfulness and given the Holy Spirit in order to enable them.
There is, therefore, a parallel between how God acted towards ancient Judah in bringing them back from Babylon and how he acts to the whole world in Christ. Ancient Israel and Judah have their counterpart in the church, which is Christ’s body and calls all people to him.