Fulton Sheen talks about the authority of the Holy Father and the grace of Infallibility that the Holy Spirit grants him in specific circumstances to guide the Church.
Our Lord introduced the principle that the first should be last and the most important should be the servant of all. The idea is that authority is for service, particularly to the least, and exercised with love. Our Lord gave Peter authority over the Church. The bishops are shepherds and can be traced back to Christ Himself. The Holy Father is infallible only when he functions as the head of the Church.