Summary: Because of the New Covenant, we become heirs of God and co-heirs with Christ. We are Blood Brothers with Jesus when we accept Jesus as sacrifice for our sins.
YOUR BLOOD BROTHER, JESUS
Jeremiah 31:31-34, "Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah— 32 not according to the covenant that I made with their fathers in the day that I took them by the hand to lead them out of the land of Egypt, My covenant which they broke, [a]though I was a husband to them, says the Lord. 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 [b]hearts; and I will be their God, and they shall be My people. 34 No more shall every man teach his neighbor, and every man his brother, saying, ‘Know the Lord,’ for they all shall know Me, from the least of them to the greatest of them, says the Lord. For I will forgive their iniquity, and their sin I will remember no more.” (NKJV)
Jeremiah 31:31-34 tells us there will be a new Covenant coming replacing the Old Covenant of sacrificing animals for the covering of sins. This new Covenant would be the final one with the sacrifice of God's only Son. When Christ shed His blood on Calvary He was actually "cutting" that New Covenant. Hebrews 9:15 tells us that Jesus is the Mediator of the New Covenant, making the old obsolete. (Hebrews 8:13) Romans 8:17 tells us we become "heirs of God and co-heirs with Christ" when we accept Jesus a Savior, thereby entering into the New Covenant. Hebrews 1:2 says that the Son has been “appointed heir of all things.” Being a co-heir with Christ means that we, as God’s adopted children, will share in the inheritance of Jesus. That also means that as a child of God and a co-heir with Christ, Jesus becomes our Brother, our Blood Brother.
THE COVENANT RELATIONSHIP
Long ago, when men would come into an agreement, they did something which guaranteed both men would keep the contract. They performed one of the oldest, most respected, and most sacred of rituals known to man. They would "cut a covenant." To cut a covenant means that the men would kill an animal and split it in half. The two halves of the animal were then spread out on the ground and the men would walk around the pieces.
THE CURSE OF COVENANT
As they walked, they would look down at the dead animal and swear that if either man ever broke the contract or covenant, the same should happen to that man, he should be split in two and die just as it happened to the animal. That was the "curse of the covenant."
THE BLESSINGS OF COVENANT
Then they would come together while standing over the two bloody halves, and, while facing each other, each man would make a small cut in one of his hands and take the other man's cut hand into his. The blood of one was now mixing with the blood of the other and, because life is in the blood, the life of one was now flowing into the life of the other. Their lives were mixing into one. Raising their clasped hands to heaven they would promise their loyalty to each other.
From that day, whatever was owned by one man became the property of the other. The strength of one now became the strength of the other. Where there were needs in one life, now those needs were met by the other. If one of them needed to to to battle with an enemy, his Blood Covenant Brother would be there to help him in the battle. If someone came to one of them to collect on a debt and the money wasn't there, each man was free to call on the other partner for help in paying the debt. Yes, for each man’s life now would become quite different. The fears of each person turned to faith in the promises of his Blood Covenant Brother.
But the blessings didn't stop with the two men. Their descendants were also included in the covenant. When one of the Blood Brothers died, his children then became the responsibility of the other brother, even children yet to be born. That is the nature of a Blood Covenant Relationship.
The Covenant was "sealed" because their blood had mixed. Now they would be considered closer than natural brothers. They had become "one" in spirit, and the scar of the cut in their hands would always remind them of their blood covenant partner and the promises made.
Friend, long before you were born, you were already included in a Blood Covenant. The Covenant was even established long before the world was created. The Covenant was between God and His only Son, Jesus Christ. You see, Adam, the first man, was created by God. Adam was made perfect, and without fault, that way he could be friends with God, who is perfectly holy and without fault. But Adam was not controlled in the way he would think, act and believe. It had to be his own decision to be a friend of God. That's just the way God is; He loved Adam so much that He would rather have Adam return His love by choice, not by a command from His Creator.