Many Catholic apologists will tell you that the difference between Protestant and Catholic boils down to one thing, authority.
Protestants claim to submit to the authority of God in the Bible alone. They claim that the Bible alone contains the Word of God and therefore, it is the only authority to which man can turn today.
Whereas, Catholic submit to the authority of God in the Church. We believe that God speaks through His Church. This is why.
1. Christ is God.
There are many Sola Scripturists, people who claim to live by the Bible alone, who deny the Divinity of Christ. They claim that they searched the Scriptures and believe that the Scriptures teach that Christ is only a man. They err because they have discarded the Sacred Tradition of Jesus Christ which is taught by the Catholic Church.
The Catholic Church, has always taught that Christ is God. Even before She wrote down the New Testament. In fact, Catholics don't need to find this fact in the Scriptures. We know it even before we read the Scriptures. The Church explicitly tells us so.
1. Christ established the Church.
Please refer to this article for more detail. The point I want to make here is that all Protestant denominations can be traced to men. And none of them lived before the year 1500.
2. Christ ordered the Church to teach what He commanded.
He didn't write anything down. Nor did He command the Church to write anything. He commanded the Church to teach by word.
3. The Church obediently taught all which Jesus commanded.
The Church taught all which Christ commanded. The lack of a Bible did not hinder the Church from teaching all which Christ commanded her to teach, infallibly.
4. The Church also wrote the New Testament to help in teaching what Jesus commanded.
In obedience to Jesus Christ, the Church began to preach and to teach all which Jesus commanded. As time progressed, those verbal lessons were also written down in order to help to advance the message of the Gospel.
5. The Church also used the Old Testament to prove the prophecies of Jesus had come true.
In imitation of Christ, the Catholic Church also used the Old Testament to prove that Jesus Christ was therein, prophecied. That Jesus Christ is the Messiah. That Jesus Christ must suffer and on the third day, rise again.
6. The Church gets its authority from God and that authority is confirmed in the Word of God, the New Testament.
Jesus Christ is God. And Jesus Christ established the Church and gave her the authority to make disciples of the world. Those who deny the Church, deny Christ. Because it is He who commanded her to Teach all which He wanted taught.
The New Testament tells you that Jesus established a Church (Matt 16:18) and that you should submit to that Church (Matt 18:17). If you claim to obey Scripture, you should obey the Church because the Bible tells you so.