There is the one Catholic Church established by Christ investing it with infallible authority to teach ONE truth for ALL times, and then there is everything else under the sun. The books in the Bible did not fall from the sky. They were assembled over nearly three hundred years by the early Church fathers and the canonical texts approved in the Synod of Rome in AD 382 remains to this day. If you doubt that infallible authority, then perhaps you must doubt whether some books were accidentally left out or included. That infallible authority did not fly out of the window at some point in time.
That's all very nice, but it doesn't answer the question posed - if the post about Christ dieing for our sins was "simplistic rot", how does one respond to what God told Jeremiah when He said that He would make a New Covenant and would forgive our wickedness and recognize our sins no more?