On the altar you are looking at the same thing as you saw there last night. You have not heard, however, what this is, what it signifies, or about the greatness of the reality of which it is a sacrament. Your eyes are looking at bread and cup. This is the evidence before your physical sight. But your faith must be instructed concerning it- this bread being Christ 's Body and the cup containing His Blood. Though perhaps these words may be enough to initiate faith, faith must be further instructed in accordance with the Prophet's words: 'Believe that you may understand'
Saint Augustine... at the beginning of the human race the woman was made of a rib taken from the side of the man while he slept; for it seemed fit that even then Christ and His Church should be foreshadowed in this event. For that sleep of the man was the death of Christ, whose side, as He hung lifeless upon the Cross, was pierced with a spear, and there flowed from it blood and water, and these we know to be the sacraments by which the Church is built up.
Saint Augustine