With Paul explaining Christianity to the Athenians, I recall something he wrote to the people of Galatia, namely “Even if an angel from heaven should preach to you a gospel other than the one we preached, let that one be accursed.”
In speaking of the gospel “we preached” he was speaking of himself as one of the apostles.
A century after Paul, there rose up an opinionated group of Christians who claimed to be the recipients of a new gospel. History has remembered them as the Gnostics, which is Greek for the “Knowing ones.” (They remind me of a grand niece of ours who resisted being told anything. She’d push it aside, saying, “I know, I know.” She was a modern day Gnostic.)
St. Irenaeus, a century after Paul, warned people against the Gnostics. He wrote, “It is in our power to contemplate clearly the tradition of the Apostles through the bishops instituted by the Apostles.”
Through the centuries the bishops have come together in councils to clearly restate the gospel Christ gave into the hands of the Apostles.
Accidentally the tradition of the Apostles became cloudy by the First Vatican Council’s declaration of papal infallibility in 1870. The cardinals of the Curia, picturing themselves as the voices of the infallible pope, began overruling the bishops.
Pope John XXIII put an end to that in 1963 by calling twenty-five hundred bishops into St. Peter’s, entrusting them with the task of clearly stating the traditions of the Apostles.