Church Fathers on Mark 14:25

When the rites of the old Passover were finished, He passed to the new, in order, that is, to substitute the Sacrament of His own Body and Blood, for the flesh and blood of the lamb. Wherefore there follows: 'And as they did eat, Jesus took bread'; that is, in order to shew that He, Himself, is that person to whom the Lord swore, 'Thou art a Priest forever after the order of Melchizedec.' [Ps 100:4]

That is, giving thanks, He brake it, which we also do, with the addition of some prayers.

But in a mystical sense, the Lord transfigures into bread His Body, which is the present Church, which is received in faith, is blessed in its number, is broken in its sufferings, is given in its examples, is taken in its doctrines; and He forms His Blood in the chalice of water and wine mingled together, that by one we may be purged from our sins, by the other redeemed from their punishment [formans sanguinem suum ap. I’seudo-Hier]. For by the blood of the lamb our houses…