Heb 8:8, Mk 14:24, Gen 15:8-10,17, Ex 24:4-8, Ps 50:5
God gave Abraham a covenant, and as a symbol of the fulfillment of that covenant, God passed through the pieces of meat. Later, when Christ died, this covenant was fulfilled. (Gen 15:8-10,17)
Gen 15:8 And he said, Lord God, whereby shall I know that I shall inherit it? 9 And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon. 10 And he took unto him all these, and divided them in the midst, and laid each piece one against another: but the birds divided he not. 17 And it came to pass, that, when the sun went down, and it was dark, behold a smoking furnace, and a burning lamp that passed between those pieces.
In the Old Testament, Moses read God's covenant and shed the blood of a sacrifice to receive the forgiveness of the people's sins. (Ex 24:4-8, Ps 50:5)
Ex 24:4 And Moses wrote all the words of the Lord, and rose up early in the morning, and builded an altar under the hill, and twelve pillars, according to the twelve tribes of Israel. 5 And he sent young men of the children of Israel, which offered burnt offerings, and sacrificed peace offerings of oxen unto the Lord. 6 And Moses took half of the blood, and put it in basons; and half of the blood he sprinkled on the altar. 7 And he took the book of the covenant, and read in the audience of the people: and they said, All that the Lord hath said will we do, and be obedient. 8 And Moses took the blood, and sprinkled it on the people, and said, Behold the blood of the covenant, which the Lord hath made with you concerning all these words.
Ps 50:5 Gather my saints together unto me; those that have made a covenant with me by sacrifice.
Just as a will is effective that the testator must die, so Christ must die for the new covenant to be effective. (Heb 9:16-22)
Heb 9:16 For where a testament is, there must also of necessity be the death of the testator. 17 For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth. 18 Whereupon neither the first testament was dedicated without blood. 19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people, 20 Saying, This is the blood of the testament which God hath enjoined unto you. 21 Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry. 22 And almost all things are by the law purged with blood; and without shedding of blood is no remission.
God promised Christ, the new covenant. And God made the new covenant into effect by shedding Jesus, the Christ, on the cross. (Heb 8:8, Mk 14:24)
Heb 8:8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
Mk 14:24 And he said unto them, This is my blood of the new testament, which is shed for many.