Matthew Henry on Luke 22:19-20

The Lord's supper is a sign or memorial of Christ already come, who by dying delivered us; his death is in special manner set before us in that ordinance, by which we are reminded of it. The breaking of Christ's body as a sacrifice for us, is therein brought to our remembrance by the breaking of bread. Nothing can be more nourishing and satisfying to the soul, than the doctrine of Christ's making atonement for sin, and the assurance of an interest in that atonement. Therefore we do this in rememberance of what He did for us, when he died for us; and for a memorial of what we do, in joining ourselves to him in an everlasting covenant. The shedding of Christ's blood, by which the atonement was made, is represented by the wine in the cup.