Arthur is referring to the Gospels, and to all those other books defined by the Catholic Church to be inspired and inerrant. We call that scripture 'the Bible'.
There's a reason why the Aquarian Gospel, the Babylonian Gospel and all those other Gnostic gospels aren't in the Bible. It's because the Catholic Church rejected them.
There are many outside of the formal Catholic Church who yet cling to the Bible, the body of scripture that the Church has declared inerrant. They implicitly trust the choices made by the Church, on the authority given it by Christ.
They,(non-catholics)implicitly trust the choices made by the Church. As you have stated is not necessarily the case. Many do not agree with the catholic churches choices and or decisions on numerous things which I think you'll see on this thread.
One thing which disturbs me about the catholic membership and clergy is that if one disagrees with the dogmas and rituals etc. of their church they are anti-catholic. I for one am not anti-catholic but I do disagree with many of their practices and claims. It just seems if you are catholic you must abide and believe in what the church determines moreso than what Christ Himself has determined...or in fact has warned against.