Catholic sources about Papacy

For men to be saved, They need to submit and follow to the Pope

"Furthermore We declare, state and define that it is absolutely necessary for the salvation of all men that they submit to the Roman Pontiff." -- Bull Unam Sanctum of Pope Boniface VIII, 1302. THE TEACHING OF THE CATHOLIC CHURCH by Neuner and Ross, S.J., p. 204, No. 342.

It is because the Pope has authority and the Vicar of Christ:

"We decree that the Holy Apostolic See and the Roman Pontiff have primacy in the whole world, and that this Roman Pontiff is the successor of blessed Peter, the Prince of the Apostles, and true "Vicar of Christ," head of the whole Church and father and teacher of all Christians..." -- Council of Florence, 1439, THE TEACHING OF THE CATHOLIC CHURCH by Neuner and Ross, S.J., p. 206, No. 349.

It is because of the succeeding Popes' statements.

1. Leo XIII (1902): "The supreme teacher in the Church is the Roman Pontiff. Union of minds, therefore, requires, together with a perfect accord in the one faith, complete submission and obedience of will to the Church and to the Roman Pontiff, as to God Himself." -- SCRIPTURES FOR ROMAN CATHOLICS by Dr. Bartholomew Brewer

2. Pius X: "The Pope is not only the representative of Jesus Christ, but He is Jesus Christ Himself hidden under the veil of flesh. Does the Pope speak? It is Jesus Christ who speaks." -- SCRIPTURES FOR ROMAN CATHOLICS by Dr. Bartholomew Brewer

3. Pius XI: "You know that I am the Holy Father, the representative of God on earth, the Vicar of Christ, which means that I am God on the earth." -- SCRIPTURES FOR ROMAN CATHOLICS by Dr. Bartholomew Brewer

 The Pope represents Jesus Christ Himself...i i. Cardinal Sarto, as quoted in Publications of the Catholic Truth Society Volume 29 (Catholic Truth Society: 1896): 11.