Rupert of Deutz, after being a monk at Liège, became Abbot of Deutz in 1120, and died there in 1135. His most important works are expositions of Holy Scripture of a highly mystical character, which are marked by great spiritual insight and power. In addition to statements of an ordinary kind as to the change and translation of the bread and wine into the real flesh and blood of Christ, which hung on the cross and flowed from His side, they contain passages of some importance on the relation of the elements to Christ’s body and blood, and of the Eucharistic presence and sacrifice to the passion of Christ.

In the mount of vision, that is, in the Holy Catholic Church, outside which no one will ever see God, the same Son is continually offered to God the Father, and yet remains immortal and impassible. For in this way of offering there is a resemblance to the sacrifice of the holy and faithful patriarch [that is, Abraham in the sacrifice of Isaac], because as in that case so also in this case there is no blood poured forth of a son slain by the hands of cruel men but the same Son abiding living and unbroken is presented to God the Father by the hands of the faithful, and is received in their mouths.… He [that is, Abraham] carries fire and sword, because without the fire of the Holy Ghost no one is worthy to approach so great a mystery, and without the sword of the word this sacrifice of salvation is not offered. Christ is present as was Isaac according to His own words of truth, ‘Where two or three are gathered together in My name, there am I in the midst of them’. … Whole is He present, whole He lies on the sacred altar, not that He may suffer again but that His passion may be presented as a memorial (memoriter reprœsentetur) to faith, to which all past things are present. Christ is again offered and yet remains impassible and living, as Isaac was offered and yet was untouched by the sword. The bread is broken for Him and is eaten; but, though that bread is now Christ Himself, yet Christ remains whole and living. How is it, you ask, that the bread which is seen is Christ? I reply: As any kind of metal, for instance gold or silver, when it is melted and liquid by strong fire, is really gold and is also said to be and is fire. For it appears to be gold, and it is what it was; and yet it is most truly called fire, and it is what it was not. Therefore assuredly the bread which is brought to and plunged in the fearful and ineffable mystery of the passion of Christ still appears to be the bread which it was, and yet in reality it is Christ, which it was not.… As Isaac was offered, and yet was not slain, so also Christ is offered, but He is sacrificed after an impassible and immortal fashion.”

‘Roast with fire,’ that is, burnt by the travail of the passion. Wherefore, because the very force of the passion gives greater strength for the resurrection, the psalmist says in the person of Christ, ‘My strength is dried up like a potsherd’. For what is a potsherd before it goes through the fire but soft mud? But from fire it gains solidity. Thus the power of Christ’s manhood as a potsherd was dry, because from the fire of the passion it grew to the power of incorruption. More fully, because the Virgin conceived Him of the Holy Ghost, who is eternal fire, and He Himself through the same Holy Ghost, as the Apostle says, offered Himself a living sacrifice to the living God, by the same fire is the roasting on the altar, for by the operation of the Holy Ghost the bread becomes the body and the wine the blood of Christ. This cannot human wisdom understand.… You must assign all to the operation of the Holy Ghost, whose work is not to destroy or corrupt any substance which He takes for His own uses but, while the good of the substance remains what it was, to add invisibly what it was not. As God did not destroy human nature when, by His operation in the Virgin’s womb, He united it to the Word, so He does not change or destroy the substance of bread and wine according to the outward species of which the five senses are cognisant, when He unites it to the body of the Word which hung on the cross and to the blood which He shed from His side. Again, as the Word sent down from on high was made flesh not by being changed into flesh but by taking flesh, so the bread and wine raised on high from below become the body and blood of Christ not by being changed into the taste of flesh or into the horror of blood but by taking invisibly the reality of each part, that is, the divine and the human, of the immortal substance which is in Christ. Therefore, as we, according to the true and Catholic belief, acknowledge that the Man who had His nature from the Virgin and hung on the cross is God, so we truly say that what we receive from the holy altar is Christ, and we proclaim it as the Lamb of God.”

He who approaches unworthily does not partake of the sufferings of Christ, and does not hold with the mouth of his mind that which he receives with the mouth of his body.… This visible Sacrament is the body and blood of Christ, which he receives with the mouth, for his unworthiness cannot destroy the worth of so great a consecration, but he does not obtain the efficacy (rem) of the Sacrament, because he does not regard the passion of Christ with his mind and with faith working by love.”

All water, whether of the sea or of rivers or of springs or of cisterns or of lakes, all water, I say, whencesoever it has been taken or produced, is one according to substance. When, therefore, whencesoever it has been taken, it is brought to the Sacrament of the crucified Lord, the reason of the faithful does not doubt that it is the very same as that which, as I said before, our Lord shed from His side. But what is it according to substance except water? Water drawn up by the roots ascends through the vines, and, gradually invigorated by the heat of the sun, becomes wine. Again, since man is made up out of the four elements, blood is in him from the substance of water. And so wine and blood are from the same substance of moisture, and to neither of these is the element of fire lacking. For blood is warm and wine is glowing. Only in colour and taste do they differ, and, since these are accidents, they are of no importance in divine acts. For substances, not accidents, are reckoned in the number of creatures.”

It is possible for one to eat unworthily, but no one ought to eat unworthily. For the bread which has once been consecrated never afterwards loses the effect of consecration or ceases to be the flesh of Christ, but it does not in any way profit one who is unworthy.”

Rupert’s treatise On the Divine Offices contains comments on the prayers and ceremonies of the ordinary and canon of the Mass in which the rite is represented as a memorial of the Incarnation and passion and resurrection and ascension of our Lord. As in his expositions of Holy Scripture, he speaks of the consecrated bread and wine as the real body and blood of Christ. The same illustration of the production of the real substance of fire from the sun by a crystal as is used by Robert Paululus occurs here. The following passages are of some special interest:—

The holy Church, offering the new and real sacrifice, offers not only the bread and wine, which are bodily seen, but also that which is not seen except by the eyes of faith, the Word of God, the Son of God.”

The matter or substance of the sacrifice which was then and now is in the hands of our High Priest is not simple, as our High Priest Himself is not of divine substance only or of human substance only. For both in the High Priest and in the sacrifice there is a divine substance and there is an earthly substance. In each there is an earthly substance, that which can be seen in a bodily or local way. In each there is a divine substance, the Word invisible, who in the beginning was God with God. For when the same High Priest, holding bread and wine, said ‘This is My body,’ ‘This is My blood,’ it was the voice of the Word incarnate, the voice of the eternal beginning, the Word of ancient counsel. The Word who had taken human nature, that is, remaining in the flesh, took the substance of bread and wine with His life as instrument and united the bread to His flesh and the wine to His blood.… The Word of the Father coming between the flesh and blood, which He took from the Virgin’s womb, and the bread and wine, which He took from the altar, makes one sacrifice. When the priest distributes this to the mouths of the faithful, the bread and wine are consumed and pass away. But the Son of the Virgin with the Word of the Father united to Him both in heaven and among men remains whole and unconsumed. But he who is without faith obtains nothing from the sacrifice besides the visible species of bread and wine.… He who eats the visible bread of the sacrifice and drives away from his heart that which is invisible by his want of faith, slays Christ, because he separates life from that which has been made alive, and with his teeth tears the dead body of the sacrifice, and in this way is guilty of the body and blood of the Lord.”

He commands these to be borne by the hands of His holy angel to His altar on high and to be in the presence of His divine majesty unlocally and invisibly. For the unlocal and invisible majesty is everywhere, His altar on high is everywhere, which is the faith of the Catholic Church.”