The Bread of Life is not really bread. The wine of the altar is not actually wine. It has become the blood of Christ. He does this by giving us his body and blood under the appearances of bread and wine. That is, only those believe this who are moved by the spirit.
Faith is a divine gift.
The Eucharist is nourishment only for believers. A priest who has not thought about and accepted these paradoxes and their application to the priesthood can hardly understand fully what it means to be a priest. The priest is not merely what he appears to be. He is, of course, a man, a human being, much like other human beings. At the same time, he is not just like other human beings.