There is then also the very famous passage from St. Cyril of Jerusalem from his Mystagogy:
"9. These things having learnt, and being fully persuaded that what seems bread is not bread, though bread by taste, but the Body of Christ; and that what seems wine is not wine, though the taste will have it so, but the Blood of Christ; and that of this David sung of old, saying, (And bread which strengtheneth man's heart, and oil to make his face to shine) [Ps. 104:15], `strengthen thine heart', partaking thereof as spiritual, and `make the face of thy soul to shine'. And so having it unveiled by a pure conscience, mayest thou behold as in a glass the glory of the Lord, and proceed from glory to glory [2 Cor. 3:18], in Christ Jesus our Lord:--To whom be honor, and might, and glory, for ever and ever. Amen."
Source: St. Cyril of Jerusalem, Mystagogic Catechesis 4,1, c. 350 A.D.