At the Last Supper when Jesus said, “This is my commandment.” He said that as part of his instituting the New Covenant. And, he was echoing what happened with Moses at Mount Sinai. Let’s look back at that.
In Chapter Nineteen of Exodus God told Moses to ask the people if they wished to enter a covenant with him, and they all said they wanted it. In the next chapter, after he had told Moses to gather the people before the mountain, God set Mt. Sinai rumbling and smoking, scaring the people half to death. He was preparing them to abide by the covenant by first putting the fear of God in them.
Then, in Exodus 24 God had Moses once again assemble the people before the mountain, this time to ratify the covenant.
In the covenant God would become one with the people, and the people would become one with God. Now, since there was no way that God could become like them, for the two parties to be united they would need to become like him. Moses led them through the process by which that union could be brought about. He shouted out the Commandments one at a time, waiting for them to agree to each.
At the same time that they were agreeing to keep the commandments, young men carrying big brass bowls of cattle blood were circulating through the crowd, sprinkling all the people with blood, then pouring what was left on God’s altar. The Jews, feeling that blood was life itself, believed that the life force in the sprinkled blood and the blood poured on God’s altar was leaping over the open spaces to join the people and God into one living People of God.At the Last Supper after Jesus had given the cup to the Apostles to make of them one people with him, he announced not the Ten Commandments, but his one commandment they would need to observe for them to become like him. He said, “This is my commandment: love one another as I have loved you.