When I was growing up, and especially as I revealed to others that I was considering becoming a priest, I was once asked, “How do you know what you believe? How do you know that it is trustworthy?” Well, unable to answer this fully myself, I went to my father as I often did in matters of faith and life. Part of his answer was that we were Catholic and this is what we believe and live as one might expect him to respond, but it also went deeper. He wanted to know what the person seemed to be asking me. He explained that there was the constant history and witness of our Faith over the last 2000 years. And he said that both God and men testify to the same Truth. Finally, he stated that is just makes sense, from which I took that the Faith was reasonable and did not contradict our reflected experience.
Indeed, this is a very good question to Roman Catholics, how do we know what we believe? And how can we be sure that we can trust it? (Fr Robert Zwilling)