Pope St. John Paul II
“The Church lives by the Eucharist, by the fullness of this Sacrament, the stupendous content and meaning of which have often been expressed in the Church’s Magisterium from the most distant times down to our own days. However, we can say with certainty that, although this teaching is sustained by the acuteness of theologians, by men of deep faith and prayer, and by ascetics and mystics, in complete fidelity to the Eucharistic mystery, it still reaches no more than the threshold, since it is incapable of grasping and translating into words what the Eucharist is in all its fullness, what is expressed by it and what is actuated by it.”
Source: Pope St. John Paul II, REDEMPTOR HOMINIS, 3/4/79