In the Old Testament, the Israelites are commanded not to consume meat that still has blood in it. In Genesis 9:4 God tells Noah he and his family could eat animals for food, and also says “But you must not eat meat that has its lifeblood still in it.” It is also mentioned various times in the Old Testament laws that consuming blood was forbidden.
Part of the reason for that was because blood represents life. In Genesis chapter 4, After Cain had killed his brother Abel, God asked Cain where Abel was, and God said his “blood cried out to me.”
After commanding that the Israelites not consume blood in Leviticus 11, God says, “For the life of the flesh is in the blood, and I have given it for you on the altar to make atonement for your souls, for it is the blood that makes atonement by the life.” In order to ensure that the blood of sacrifices would always be considered special, he didn’t allow blood to be included in common food.
Also, blood was the only atonement for sin, so it was considered sacred. Atonement means to make amends, which is what the sacrifices did for the Israelites, it made amends for their sins. And the Israelites were not to defile anything that was sacred (which is why they had so many laws to purify themselves when they became unclean).
So when it comes to Jesus and taking communion/the Lord’s supper, Jesus is telling us to partake in his blood because he is literally giving us his life, and it is a remembrance that he gave his life for us. In John 6 he says, “For my flesh is true food, and my blood is true drink. Whoever feeds on my flesh and drinks my blood abides in me, and I in him.”
Jesus is in essence saying that communion is the act of Jesus’ perfect life and sacrifice being transferred to us. So you can imagine how radical this would have sounded to a 1st century Jew.
So again with Jesus, we see that his blood is the atonement for our sins, and so Christians (and everyone) are invited to seek Jesus for the grace and mercy Jesus offers.
The act of communion does not actually save or forgive anyone, but it is a representation that through Jesus, we are atoned for and forgiven. When we take communion, we are accepting the fact that Jesus is our sacrifice.
Jesus is not violating God’s law in calling Christians to remember his sacrifice through communion, instead he is fulfilling God’s plan of redemption, inviting everyone to enjoy God’s forgiveness and grace.