Take this, this is my body. This is my blood of the covenant, which is poured out for many. And all this is an explanation of what happens on Calvary. Jesus knew the plotting against him. Jesus could have avoided Jerusalem or escaped Jerusalem, but he had to show that there was nothing the Son of God would not do for humankind.
Body given and blood shared at the meal is for the disciples.
The message, the explanation, is the same for us today. But we need to be reminded of this. In our first reading we hear of Moses gathering the people of Israel and reminding them of all that the Lord was saying and asking of them. The people said they were willing to live according to the Word of God and Moses celebrated that covenant, that agreement, that bond, with the pouring and the sprinkling of the blood. We gather week after week to remember what God has done for us in the person of Jesus.