During the last supper Jesus invited his disciples to join him in a celebration of Passover (as he was Jewish). The Eucharist had been celebrated by the Jewish as remembrance of the Hebrews being saved and passed over by the grace of God.
During the meal Jesus broke and shared around a piece of unleavened bread, he added the words ‘This is my body, which will be given up for you’. Then as he passed around the wine he said ‘This is my blood which will be poured out for you’.
This is a symbol of Jesus sacrificing himself to all his followers as he becomes the sacrificial lamb when his blood was split on the cross and his deliverance of his people from death.