While they were eating, Jesus took a piece of bread, gave a prayer of thanks, broke it, and gave it to his disciples. “Take it,” he said, “this is my body.”
Those who think highly of a certain day do so in honor of the Lord; those who will eat anything do so in honor of the Lord, because they give thanks to God for the food. Those who refuse to eat certain things do so in honor of the Lord, and they give thanks to God.
The cup we use in the Lord's Supper and for which we give thanks to God: when we drink from it, we are sharing in the blood of Christ. And the bread we break: when we eat it, we are sharing in the body of Christ.