Or history?
If one was Christian for the first 1000 years of Christianity, one was Catholic. That's all there was. Then, in 1054 A.D., the Orthodox splintered off, but retained Apostolic Succession.
Protestantism didn't arise until the 16th century and was started by rogue Catholics. Every one of the Protestant Reformers were Catholic. That means one has to ask the question, was Christianity wrong for 16 centuries until Protestantism arose, and came to "correct" the teachings? And if so, which of the tens of thousands of man-made, doctrinally contradicting denominations has it right? Or do you claim no one does and Christ reallyl did a poor job of spreading His message?
We claim that Christ founded a (one!) Church, which has existed the entire time. It alone has the fullness of Christ's truths, which it does not claim the right to change. Christ founded a Church to spread His truths. He didn't write a book. The Church He founded wrote the New Testament, but didn't set the canon for the New Testament until the late 4th century. The vast, vast majority of people were illiterate anyway, until the last 100 years, give or take, in man's history. St. Paul refers to the Church as the "pillar and foundation of truth" in 1 Tim 3:15.