If the heavenly word was effectual in the earthly spring, if it was effectual in other things, is it not effectual in the heavenly sacraments? Therefore thou hast learnt that what was bread becomes the body of Christ, and that wine and water are put into the chalice, but become blood by the consecration of the heavenly word…
Wilt thou know that it is consecrated by heavenly words ? Hear what the words are. The priest speaks, “Make for us,” he says, “this oblation approved, ratified, reasonable, acceptable, seeing that it is the figure of the body and blood of our Lord Jesus Christ, who the day before he suffered took bread in his holy hands, and looked up to heaven to thee, holy Father, almighty, everlasting God, and giving thanks, he blessed, brake, and having broken, delivered it to his apostles and to his disciples, saying, Take, and eat ye all of this; for this is my body, which shall be broken for many.
Likewise also after supper, the day before he suffered, he took the cup, looked up to heaven to thee, holy Father, almighty, everlasting God, and giving thanks, blessed it and delivered it to his apostles and to his disciples, saying, Take, and drink ye all of this ; for this is my blood.” Observe all those expressions. Those words are the Evangelists’ up to Take, whether the body or the blood. After that they are the words of Christ ; Take, and drink ye all of this; for this is my blood. And observe them in detail.
Who the day before he suffered, he says, in his holy hands took bread. Before it is consecrated, it is bread, but when the words of Christ have been added, it is the body of Christ. Therefore hear him saying : Take and eat ye all of this ; for this is my body. And before the words of Christ it is a cup full of wine and water. When the words of Christ have operated then and there it is made to be the blood of Christ which redeemed the people. Therefore, see in how many ways the word of Christ is mighty to change all things. There the Lord Jesus himself testifies to us that we receive his body and blood. Ought we to doubt of his trustworthiness and testimony?
Now come back with me to the point which I set out to prove. It is a great and awful thing that he rained manna on the Jews from heaven. But distinguish. What is greater, manna from heaven or the body of Christ? Certainly the body of Christ who is the maker of heaven. Then he who ate manna died. Whosoever eats this body shall have remission of sins and shall never die.
Therefore [when thou receivest] it is not superfluous that thou sayest Amen, already in spirit confessing that thou receivest the body of Christ. The priest says to thee, to thee, The body of Christ. And thou sayest, Amen, that is, true. What the tongue confesses let the heart hold fast…
Give us this day our daily bread. I remember my sermon when I was dealing with the Sacraments. I said to you that before the words of Christ that which is offered is called bread : when the words of Christ have been uttered, it is no longer called bread, but is named body. Why then in the Lord’s Prayer, which follows afterwards, does he say : Our bread ? He called it bread indeed, but he called it … supersubstantial. It is not the bread which passes into the body, but that bread of eternal life, which supports the substance of our soul… The Latin … calls this bread “daily which the Greeks call “coming.” Therefore what the Latin and what the Greek text said seem both useful. The Greek indicated both in one expression, the Latin said “daily.” If it is daily bread, why dost thou take it once a year …? Take daily what is to profit thee daily. So live that thou mayest deserve to receive it daily. He who does not deserve to receive it daily, does not deserve to receive it once a year; as holy Job offered sacrifice daily for his sons, lest perchance they should have done any sin in heart or word. Therefore dost thou hear that as often as sacrifice is offered, the Lord’s death, the Lord’s resurrection, the Lord’s ascension and the remission of sins is signified, and dost thou not take this bread of life daily? He who has a wound needs a medicine. The wound is that we are under sin ; the medicine is the heavenly and venerable sacrament.
Give us this day our daily bread. If thou receives daily, “this day” is “daily” to thee. If Christ is for thee “this day,” he rises again for thee “daily.” How? Thou art my Son, this day have I begotten thee. Therefore “this day” is when Christ rises again. Yesterday and to-day he himself is, says the Apostle Paul. But in another place he says, The night is far spent, the day is at hand? Yesternight is far spent, the present day is at hand. Source: “On the Sacraments,” Book 4.4 & 5; 5.4, by St. Ambrose of Milan(340 – 397)