On Mondays, I answer questions frequently asked by those considering a return to the Catholic Church. How do I know this stuff? I was away for more than 30 years myself, and am the co-author of When They Come Home: Ways to Welcome Returning Catholics, a book for pastors and parish leaders interested in this ministry.
Why do Catholics believe the pope is perfect?
We don’t believe the pope is perfect. People often don’t understand what papal infallibility means, so let’s start there.
We recognize and accept that on occasion, the pope is presented with a divine revelation of doctrine. When this happens—also termed ex cathedra, or speaking from the position that was once held by St. Peter himself—Catholics must accept this teaching 
concerning faith or morals without question. Most recent examples of this occurred in 1854 when Pope Pius IX declared that Mary is the Immaculate Conception, born without sin, and in 1950, when Pope Pius XII declared that the Blessed Virgin was assumed body and spirit into heaven upon her death.
This does not mean the pope is incapable of human error, or that every word that falls from his lips is divinely inspired. For example, encyclicals are not presented as being dogma. There is dispute among theologians over whether canonization announcements are in fact infallible. As Pope Benedict XVI said in July 2005, “The pope is not an oracle; he is infallible in very rare situations, as we know.”
That said, the pope is the leader of the worldwide Church. He is a learned, respected man, selected by the Sacred College of Cardinals. Any statement or teaching by the pope should be considered prayerfully and seriously.
Infallibility does not rest solely with the pope. If the bishops of the world through their teaching office (called the Magisterium) in concert with the pope issue a doctrine that is divinely revealed, we must accept it. Examples of teachings that are “irreformable” in this way include the sacraments and beliefs regarding sin and grace, Mary, and Jesus.
Even statements that are not issued ex cathedra but that the Church declares to be logical outgrowths of divine revelation require a submission of intellect and will from the faithful. Examples include our strong belief that all life is precious from conception to natural death and papal infallibility.
