Heb 8:10, Rom 6:3-7
In the Old Testament, Jeremiah prophesied that the captives of Israel would be set free and united with God's eternal covenant. (Jeremiah 50:5)
Jeremiah 50:5 They shall ask the way to Zion with their faces thitherward, saying, Come, and let us join ourselves to the Lord in a perpetual covenant that shall not be forgotten.
After that day, God said that He would write the word of God in the hearts of the people of Israel and make the people of Israel God's people. (Hebrews 8:10)
Hebrews 8:10 For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
We are united to Christ Jesus by dying for us. (Romans 6:3-7)
Romans 6:3 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? 4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: 6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. 7 For he that is dead is freed from sin.