1 Even of itself the teaching of the Blessed Paul is sufficient to give you a full assurance concerning those Divine Mysteries, of which having been deemed worthy, you have become of the same body and blood with Christ. For you have just heard him say distinctly, That our Lord Jesus Christ in the night in which He was betrayed, took bread, and when He had given thanks He broke it, and gave to His disciples, saying, Take, eat, this is My Body: and having taken the cup and given thanks, He said, Take, drink, this is My Blood. 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: Catechetical Lectures (New Advent)