In Jeremiah 31, Israel had been taken captive by Nebuchadnezzar. God was speaking to Jeremiah about Israel return to the promised land. What God was saying was double edged. Just like the two-edged sword that is the word of God, it cuts both ways. It says if they repent, God will give them back the land. But God made a new covenant with us. He said, He would write His laws and commandments on our hearts and minds. So, we would know who He is from birth. And God said, he would forgive our sins and remember them no more, repentance, forgiveness and assurance. God’s plan has been in affect for 1000’s of years. All God needed was someone to pay the price for mankind. And God found that person, 500 years later, Jesus Christ the righteous. All of this is in Jeremiah 31. Jesus came preaching using the old testament, for all the promises of God are there, long before the new testament was written.