1) The subset of Christian written tradition is Luther's reduced Old Testament canon. Moreover, even when formally accepting the New Testament canon, Luther ridiculed the Letter of James and argued against retaining some others, I forget which. This engendered selective reading of even the New Testament. The protestants rarely if ever rely on James for their instruction, ignore or spin away Christ's teaching on charity, offer fantastic interpretations of the parables, or the clear teaching on judgement based on works in the Apocalypse. 90% of Protestant argumentation from scripture revolves around isolated verses from Paul taken out of their historical, and often literal context.
The only Church Father studied with any consistency is St. Augustine, and he is taken in isolation from the other patristic literature, and his own clarifications regarding the free will are ignored. This is not the patristic approach. Contrary to Luther, the Church teaches that individual fathers erred here and there, and this is why they are not in the canon. Yet, the consensus of the Church Fathers is the sacred written tradition.
2) Sola scriptura is Luther's doctrine, at it means exatly what I say: that man is capable of understanding Luther's reduced canon outside of the entire Tradition, written and unwritten, that lives in the Church. While he was correct in criticizing indulgencies, they were not a part of the Sacred Tradition. Sola scriptura and the sale of indulgences does not justify sola scriptura.
3) Let me correct my formulation: the third error is that man's faith is a binary condition that once obtained does not alter the final salvation of the soul.
4) The distinction I draw is between grace that substantially and often gradually transforms man onto holiness, and Luther's "grace" that covers up depravity without actually removing it. The latter is an error. The former is consistent with the Tradition, written and unwritten.
I mean,
Sola scriptura and the sale of indulgences have nothing in common logically
or if you wish,
the error of the sale of indulgences does not justify the much graver error of sola scriptura
Catholics, OTOH spend too much time emphasizing the works believing that if they do all sorts of things this buys something. It should be noted that Abraham was saved by his faith 17 years prior to being saved by his works. Queen Esther was called, as far as we know, for one particular task and that was to save the Jews on one specific day. Isaiah was called to harden the people's heart so that no one would come to God. (How would you like that ministry-one that you would never see any fruit.) Works is a manifestation of the grace we have received and it can come in many forms. The Catholics, IMO, have this exactly backwards by saying we receive grace by our works.
I don't think "sola scriptura" is ONLY Luther's doctrine. I've read a number (not all) of early church writings and time and again they point to scripture as verification of their ideas, rarely to other contemporary theologian. There is some to be sure but not much. Many of the early church fathers based their theology directly upon scripture verses.
Sola scriptura is simply a beachmark by which sound theology should be measured. It isn't doing away with the church writings of which Luther and Calvin rely heavily on. It is merely stating that one should not willy-nilly accept what is being taught and go back to the scripture to see if these things are accurate. Had many of the cardinals and the Pope followed this advice the Reformation probably would never have happened.
Protestantism makes a distinction between man's spiritual depravity and his natural depravity. Both are dead to sin. God resurrects the spirit to a newness of life and cause us to walk in His statutes and obey His ordiences. This was His divine promise. However the body is still corruptable and we wait for the glorification of the body.
Please consider me, along with Luther, a heretic as regards to enough of your dogma for us to reach that conclusion; God will view us differently; we have the One Mediator as our public defender; that not of ourselves but a gift from God.