St. Thomas Aquinas
“The presence of Christ’s true body and blood in this sacrament cannot be detected by sense, nor understanding, but by faith alone, which rests upon Divine authority. Hence, on Lk. 22:19: ‘This is My body which shall be delivered up for you,’ Cyril says: ‘Doubt not whether this be true; but take rather the Saviour’s words with faith; for since He is the Truth, He lieth not.'”
Source: St. Thomas Aquinas, Summa Theologica