Because we, like the children of Israel, were not one with God and did not have the heart to do God's will or take His good pleasure, we offended God, transgressed His ordinances, and committed sins against His commandments. We were a people whose heart was deceitful and incurable (17:9). We were exposed as having a nature that is sinful and rebellious, a nature that, like the Ethiopian's skin and the leopard's spots, could not be changed (13:23). Since this was our situation, how could we be reconciled to God? How could we be justified by Him and taken by Him to be His people?
Jeremiah gives us the answer in 23:5 and 6. "Behold, days are coming, / Declares Jehovah, / When I will raise up to David a righteous Shoot; / And He will reign as King and act prudently / And will execute judgment and righteousness in the land. / In His days Judah will be saved, / And Israel will dwell securely; / And this is His name by which He will be called, / Jehovah our righteousness." The only way that we can be reconciled to God and justified by Him is by Christ, the new Sprout, the righteous Shoot, who is called Jehovah our righteousness. As the righteous Shoot, He came in the flesh as the descendant of David to die on the cross and shed His blood in order to accomplish redemption for our justification.
Based upon Christ's redemption we have been justified, and the Triune God has come into us to be our life, our person, and our everything. This creates a situation in which God is free to work out His eternal economy in us by His dispensing of Himself into our being. If we see this principle and grasp it, we will understand the entire book of Jeremiah.
The book of Jeremiah was not written according to the historical sequence, but this book surely has a spiritual sequence. First, Jeremiah shows us the basic sins of God's people—forsaking God and hewing out their own cisterns. Then the human heart is gradually exposed as being deceitful and incurable. We are wicked and hopeless, having a fallen nature that cannot change. In order to be one with God, we need Christ as the Shoot of David to be our redemption and justification. This ushers the Triune God into us to be our life, our inner life law, our capacity, and our everything. This is the new covenant (31:33). In the new covenant, we do not do anything. Rather, we are simply one with God to let Him write Himself into us as the law of life. This law of life implies the Triune God with the highest capacity for our function. God lives in us and has the freedom, in matters great and small, to dispense Himself into our being to carry out His economy. This dispensing will bring in the restoration of all things and will consummate in the New Jerusalem in the new heaven and new earth. The New Jerusalem is the consummation of the economy of God accomplished by His eternal dispensing.
In Jeremiah we see that we are redeemed, that we are justified, and that we have become one with God. Eventually we will know God, live God, and be constituted with God in His life and nature that we may be His corporate expression. This is the complete teaching of the Bible, especially in the New Testament, and this is the essence of the book of Jeremiah.