Benedict made the comments during a meeting with thousands of young people in St. Peter's Square during which he took questions from five students on issues such as the family, how to read the Bible and faith and reason.
Asked by one student how he realized his own priestly vocation, the 78-year-old pontiff said that when he was young in Germany it was more "normal" to accept faith and vocations than it is today.
"There was the Nazi regime," Benedict said. "We were told very loudly that in the new Germany 'there will not be anymore priests, there will be no more consecrated life, we don't need this anymore, find another profession."'
"But actually hearing these loud voices, I understood that in confronting the brutality of this system, this inhuman face, that there is a need for priests, precisely as a contrast to this anti-human culture," he said.
Benedict was enrolled in the Hitler Youth as a teen and later deserted from the German army near the end of World War II.
The pope acknowledged that he had doubts about the commitment required for joining the priesthood and whether his love for theology alone was enough of a reason to become ordained.
"I asked myself if I really had the capacity to live an entirely celibate life," he said. "Being a theoretical and not practical man, I also knew it wasn't enough to love theology to be a good priest, but I also needed to be available to young people, old, sick and poor people."
He said that in the end, God as well as friends and other priests helped him to decide.
The meeting was Benedict's second in which he has publicly fielded questions from young Catholics. Benedict also has met several times with priests in informal town-hall style question-and-answer sessions.
Benedict was asked how Catholics can harmonize the apparent conflict between faith and reason. He gave a highly philosophical response that touched on mathematics, chaos theory and the "intelligent design" behind creation.
In November, Benedict waded indirectly into the evolution debate in the United States, saying the universe was made by an "intelligent project" and criticizing those who in the name of science say its creation was without direction or order.
At the end of the meeting, Benedict joined a few young people at the tomb of Pope John Paul II to pray, concluding the Vatican's commemorations of the first anniversary of the pontiff's death.