Because sin had entered the world through Adam and Eve, God's plan provided a way for man to come back into the presence of the Holy God. God provided a way through the shedding of blood. A sacrifice had to be made. God would give man a preview of that plan through the system of blood sacrifices in the Old Testament. In Numbers 28-29, God called for 1,273 public sacrifices a year-each morning and evening, each Sabbath, the first day of each month and during the special feasts days of assembly and celebration. In addition to the public sacrifices, there would also be individual sacrifices. This must have been a continual blood bath as blood ran from the altar.
The offering had to be spotless and with no defects or blemishes. As the animal is killed, the blood is caught and then sprinkled by the priest on the horns of the altar and poured out at the base of the altar.
One day a year was celebrated as the Day of Atonement. On this day the High Priest would offer a sacrifice for the sins of the nation. These sins were symbolically transferred to the spotless, blameless lamb dying in the place of the people and became the sin subsititute for the collective sins of the Jewish nation. The High Priest after offering an animal sacrifice for his own sins, would take the blood of the lamb into the Holy of Holies.
Only one is allowed behind the veil, the curtain separating the people from the presence of God. Only one can present the blood before God. If for some reason the High Priest dies while he is behind the veil, no one is allowed to go in to get him. God would strike them dead on the spot.
In the Holy of Holies the High Priest must sprinkle the blood on the Ark of the Covenant. God either accepts or rejects the offering. If God rejects the sacrifice, the High Priest is struck dead. If God accepts the sacrifice, the High Priest returns to the people and rejoicing takes place. The people knew their sins were forgiven for another year.
Jesus was both the High Priest and the Lamb of God. He was the blameless lamb sacrificed for the sins of the nations. He was the High Priest who carried His blood before the Father and presented it as atonement for our sins. This is what John the Baptist meant when he said:
John 1:29 “Behold! The Lamb of God who takes away the sin of the world!"