Already shortly before the exile, Jeremiah spoke of the messianic age as a time of renewed relationship between God and His people. The very concept of a new, messianic covenant-union is connected with the revelation received by Jeremiah. Ezekiel speaks of the same thing: new relationships between God and a person, as well as between God and the people of God as a whole, presuppose a change in the spiritual quality of each concrete person. This is what the prophet speaks about when he mentions a "new heart" and a "new spirit": for the heart, according to general biblical usage, denotes the spiritual center of the human person, while the breath ("spirit") that God breathed into the human being's "nostrils" at creation constitutes the personal spiritual dynamism that determines what a person will be before God. And if the heart is not brought to life, if it is left "stone," as in a fallen human being, no renewal of relationships will result.
This understanding was especially relevant against the background of those popular ideas about the Messiah and the Kingdom that saw in the Messiah only a righteous king, and in the Kingdom an ordinary earthly state where justice reigns and where correct laws, corresponding to the Torah, have been established. The prophets, as we can see, never tired of reminding people that no state, no rulers, and no laws by themselves are capable of changing human nature or freeing fallen humanity from sin. And without such liberation there can be no question of life in the Kingdom.