Jeremiah 31

Jeremiah 31:30:
“But every one shall die for his own iniquity; every man who eats the sour grapes, his teeth shall be set on edge.”

God was speaking of a new day that would be coming, when He would introduce a new covenant. Under this new covenant, everyone would be held accountable for their own sin. If you choose to live in disobedience to God and His law, you are the one who will be called to give an account. To simplify the whole thing, we could say, “you reap what you sow.” I believe this has at least a double fulfillment or application.
1- If you choose to disobey God and live a life of wickedness, it will come down upon your own head in this life.
A- “Those who plow iniquity and sow trouble reap the same, Job 4:8.
B- Hosea 8:7, “They sow the wind and reap the whirlwind.”
C- Galatians 6:7, “Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap.”
2- If we choose to reject God and His Word in this life, we will suffer His wrath and condemnation in the life to come.
A- Galatians 6:8, “For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life.”
B- John 3:18b, “But he who does not believe is condemned already, because he has not believed in the name of the only begotten Son of God.”

-Lyndon Stimeling

Jeremiah 31:33:
But this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people.

Part of the promise of the gospel is that we find the law written on our hearts – no longer an external word of condemnation, but the (super)natural desire of the new self, of faith, to act in love towards God and neighbor.
This is what is new about Jesus’ command: it no longer belongs to the economy of law, of “do this and you will live”, but to the economy of the gospel: “you will do this, often without even realizing it, because you have already been made alive through the death and resurrection of Jesus to which you are united in your baptism”.