"My sweetest Lord, my most amiable Saviour, I am now visiting Thee on this altar; but Thou returnest me the visit with far other love when Thou enterest my soul in the Holy Communion. Thou art then not only present to me, but Thou becomest my food; Thou unitest and givest Thy whole self to [...]
"It is evident to sense that all the accidents of the bread and wine remain after the consecration. And this is reasonably done by Divine providence. First of all, because it is not customary, but horrible, for men to eat human flesh, and to drink blood. And therefore Christ's flesh and blood are set before [...]
"It is absolutely necessary to confess according to Catholic faith that the entire Christ is in this sacrament." Source: St. Thomas Aquinas, Summa Theologica
"Since then He Himself declared and said of the Bread, This is My Body, who shall dare to doubt any longer? And since He has Himself affirmed and said, This is My Blood, who shall ever hesitate, saying, that it is not His blood?" Source: St. Cyril of Jerusalem, Catechetical Lectures [...]
"Augustine says in his book on the Sentences of Prosper (Lanfranc, De Corp. et Sang. Dom. xiii): 'Under the species which we behold, of bread and wine, we honor invisible things, i.e. flesh and blood.'" Source: St. Thomas Aquinas, Summa Theologica
"Consequently, no natural or created agent can act except by changing the form in something; and on this account every change made according to nature's laws is a formal change. But God is infinite act… hence His action extends to the whole nature of being. Therefore He can work not only formal conversion, so that [...]
"Some have held that the substance of the bread and wine remains in this sacrament after the consecration. But this opinion cannot stand: first of all, because by such an opinion the truth of this sacrament is destroyed, to which it belongs that Christ's true body exists in this sacrament; which indeed was not there [...]
"The sparrow, says David, finds a dwelling in houses; turtle-doves in nests; but Thou, my King and my God, hast made Thyself a nest and found a dwelling on earth on our altars, that we might find Thee, and that Thou mightest dwell amongst us. Lord, we cannot but say, that Thou art too much [...]
"Non manifete, sed quasi in occulto - 'Not publicly, but as if He would keep Himself hidden': thus goes Jesus to the feast of Tabernacles. Thus will He go on the way to Emmaus with Cleophas and his companion. Thus will He be seen after His Resurrection by Mary Magdalene. And thus will He appear [...]
"Some men accordingly, not paying heed to these things, have contended that Christ's body and blood are not in this sacrament except as in a sign, a thing to be rejected as heretical, since it is contrary to Christ's words." Source: St. Thomas Aquinas, Summa Theologica