While they were eating, Jesus took bread, and when he had given thanks, he broke it and gave it to his disciples, saying, “Take it; this is my body.” Then he took a cup, and when he had given thanks, he gave it to them, and they all drank from it. “This is my blood of the covenant, which is poured out for many” (Mark 14:22-24).
In the ancient world, serious agreements (covenants) were sealed by slaughtering animals and cutting them in half. Participants in the agreement walked between the halves and then burned them in sacrifice (see Jeremiah 34:17-20). The notion was: “If we do not fulfill our part of this agreement, may we become as this animal.”
Whenever I read this passage in Mark 14, I am reminded of a story in Genesis 15. There, in a crisis of faith, Abraham asks how he can believe God will make good on his promises. God has him to prepare several animals for sacrifice, cutting them in half. But Abraham is not asked to walk between them. Instead, God, in a flame of fire, passes between them and burns them up in sacrifice. The point is this: God is making a covenant with Abraham, a covenant guaranteed solely by God and his wholly by His being.
When we become God’s children, we enter into an agreement with God, an agreement so serious it is guaranteed by the sacrifice of God Himself – signified by the blood of Jesus. This event in Mark 14 is Christ’s initiation of the Lord’s Supper. Our observance of that Supper each week is a reminder not only of Christ’s death, but also of His covenant with us and the promises of that covenant. It is also a reminder that those promises, so integral to the covenant, are guaranteed by the life of God himself.