VATICAN CITY, August 26 (CNA/EWTN News) .- Pope Benedict XVI said Sunday that a lack of sincerity in life is "the mark of the devil" as witnessed in the decision of Judas Iscariot to continue following Jesus Christ even after he had ceased to believe in him.

"The problem is that Judas did not go away, and his most serious fault was falsehood, which is the mark of the devil. This is why Jesus said to the Twelve: 'One of you is a devil'," said the Pope in his midday Angelus address to pilgrims at Castel Gandolfo Aug. 26.

The pontiff said that Catholics pray to the Virgin Mary to help them to believe in Jesus as St. Peter did and "to be always sincere with him and with all people."

The Pope continued his recent weeks' reflections upon Jesus's "Bread of Life" discourse as delivered in the synagogue of Capernaum.

After Christ declared himself to be "the living bread which came down from heaven" many of those who had followed him, records St. John in his Gospel, "drew back and no longer went about with him."

Asked by Jesus if they too will leave, St. Peter replied on behalf of the Twelve "Lord, to whom shall we go? You have the words of eternal life."

The one exception, said Pope Benedict, was Judas Iscariot who "could have left, as many of the disciples did; indeed, he would have left if he were honest." Instead, he chose to remain with Jesus. Not because of faith or love, said the Pope, but out of a secret desire to take vengeance on his master.

"Because Judas felt betrayed by Jesus, and decided that he in turn would betray him. Judas was a Zealot, and wanted a triumphant Messiah, who would lead a revolt against the Romans." Jesus, however, "had disappointed those expectations."

The Pope, turning to the 11 apostles who did believe, reminded pilgrims of "a beautiful commentary" of St. Augustine in which the Church Father observed how St. Peter "believed and understood."

"He does not say we have understood and believed, but we believed and understood. We have believed in order to be able to understand," wrote St. Augustine in his Commentary on the Gospel of John.

After reciting the Angelus, the Pope expressed some special words of welcome to the new class of seminarians at Rome's Pontifical North American College.

"Dear seminarians, use your time in Rome to conform yourselves more completely to Christ. Indeed, may all of us remain faithful to the Lord, even when our faith in his teachings is tested. May God bless you all!"