Protestant
Why do Catholics believe in the Pope?
Christ gave Peter alone the keys of the kingdom and the charge to strengthen his brethren, establishing a permanent office of unity that the Bishop of Rome, Peter's successor, continues to fulfill.
Catholic teaching
The papacy is not an add-on to the Church but the visible principle of unity Christ instituted in Peter. The Pope, as Bishop of Rome, exercises Peter's Petrine ministry of confirming the faith and safeguarding communion among the churches.
Biblical foundation
Christ renamed Simon 'Rock' and built his Church on him, giving him alone the keys of the kingdom (Matt 16:18-19), and singled him out to 'strengthen your brethren' (Luke 22:32) and to feed his sheep (John 21:15-17).
Scripture references
Historical evidence
From St. Clement of Rome's first-century intervention in the Corinthian church to the appeals made to Rome throughout the patristic era, the early Church consistently recognized a unique authority in the See of Peter.
The Church Fathers
“With this Church, because of its more powerful preeminence, every Church must agree.”