Jo and I gave the scriptural and patristic support for the doctrine of Purgatory in 8437 and 8433. It leaves room for some doctrinal development, which the chair of Peter duly performed, but the fundamentals of the doctrine are quite patristic.
"Doctrinal development" is nothing more than a majority of old guys sitting around concurring on a tiny snippet of uninspired text. Majority wins. It becomes unchanging doctrine until the next bunch of old guys come alone and see something else. Then they have to say that the first bunch of old guys "...weren't really wrong but what they meant to say was...".
Sometimes this is innocent error. Augustine talks about how the early church was confused by baptism. At first they thought once you were baptized, you had to live a perfect life. Ten seconds after the first baptism proved them wrong. Then they though they should wait until they were close to death to be baptized, that would guarantee living a perfect life. Trouble was with this approach was that people sometimes died before they could be baptized (not a pleasant thought and probably a reason Augustine never spoke out about purgatory). But what was worst sometimes people recovered and then that meant they had to live a perfect life!!! The Church finally concluded that baptism was meant as a sign.
However, I'm not sure if all errors introduced is innocent. The Catholic Church in the 1200s was desperate for money and people were leaving. What better way to keep people around than to decree the only way to receive God's grace is through the Eucharist given directly to you by a priest, confessions had to be directly through a priest and salvation was only through the Church? This certainly would make the superstitious people in the Middle Ages go to Church now wouldn't it? In 1400, in need of cash, a fund raiser was started through indulgence.
Error upon error.
The Pope issue a decree from the chair of Peter that if you pay for your indulgences it was automatic release from purgatory; signed and sealed by Pope Leo himself, unbreakable. About a hundred years later the Catholic Church reversed itself and said the practice was wrong and those decrees meaningless. Once again, signed and sealed from the "infallible" chair of Peter. After a decree has been issued from the chair which is suppose to be infallible and binding??? How could this be???
The inspired word of God says nothing about purgatory, indulgences, the worship of Mary, venerating saints, on and on and on. These are all fantasies dreamed up by some who had too much time on their hands-voted on and properly recorded by the majority. It doesn't matter if the majority was wrong or what the intent was for issuing a decree.
I'm not going to go back through four months of material but simply reiterate what I stated before; I doubt if any of us would believe for a moment that while John was sitting on the island of Patmos, he was asking for Mary's intercession or praying to Peter or Paul for strength. Yet this is what the Church teaches.