The Roman Catholic Church at the beginning of the 16th century was in shambles theologically. The teachings of the church were very far away from the truth and they were leading people into a false faith, and in essence damming them to hell. Here is a breakdown of what was being taught.
There was a comparison in their view of salvation to that of a scale; the good you do, and the other the bad For a person to go to heaven the good needed to outweigh the bad.
The bad side of the scale is weighed down by mortal sins and by venial sins. Mortal sins are the deadly sins that send a person to hell. These sins can only be forgiven by God. Venial sins are just things that are bad for you but won't damn you to hell. If any venial sins are left unconfessed and unforgiven the sinner is sent to purgatory where the penalty is worked off.
The Good side included all the good works that you did and the work of Christ on the cross. Both are necessary for salvation. But the work of Christ is not enough for your salvation. There must be good works in your life, works that will tilt the balance of the scales toward the good. Any venial sins that are unforgiven are accounted for by good works.
The Catholic church dicatated what these good works were and also reserved the right to openly forgive any and all sins. This lead to the rise of indulgences. Through a progression of sorts that arrises out of the crusades which at the end, a person could buy forgiveness for venial sins and other trivial matters. This climaxed when a monk began to sell indulgences for any sin; mortal or venal.
Martin Luther was reading throught Psalms 31 and the book of Romans and he said that the just live by faith. He saw what the Catholic Church was doing when it was selling indulgences and saying that your good works out weigh your bad works, and said it was wrong. It is faith in Jesus' work of redemption that saves us, not through good works not through buying indulgences from the church, and definately not through our own merrit.
He published his problems with the practice of indulgences in his 95 Thesis which he wrote in 1517. His work led to the Prodestant Reformation, which lead to the fall of the power of the Roman Catholic Church. This reformatation also lead to the movement which the church I now attend is a part of.
I sit here today almost 500 years later, and i catch myself falling into the pattern of the Catholic's of Luther's day. I try and base my salvation on what I do. But the Bible says that all our righteousness is as filthy rags, so obvously that won't work for us. We have to place all our faith in God, and not what we do.
But I continously forget this, and try and work my way into being a good Christian. I forget it's about my faith and in Christ and i make it how good I am. And when I have not been good, I wonder if I am no longer a Christian. It is not about my actions as much as it is about my faith.