During the eating of the Old Testament Passover lamb with the disciples, the Messiah instituted NEW ordinances , to replace the old ones. Notice that Luke shows that the Messiah attached no special significance to this cup. The bread, which followed, He did make special, symbolizing His body given for us, verse 19 . It was this cup, after supper, that joined the earlier symbolic bread, to become part of the New Testament Passover. The institution of the Passover in Exodus 12 shows only the Passover lamb, unleavened bread, and bitter herbs.
Nothing is said about cups of wine with Passover.
This was a Jewish tradition added later. By the first century A.D., the Passover service had the hymns, hand washing and four cups of wine. They were in a reclining position, so John could virtually lean on the Master's breast. Luke mentions two of the four cups, the first and the third. Early Jewish tradition says these were the most important.