First let us remember that an indulgence
cannot forgive a sin, nor could it ever. An indulgence
remits the temporal punishment due to a sin that (has arlready been committed, not future sins) is already forgiven. Or an indulgence pre-supposes the sin has already been forgiven, like when we today commit grave sin and ask forgivness(from God, saying a perfect act of contrition) before we go to confession. Luther was unable to follow the rules of monastic life and grew, little by little to resent the Church teachings and disciplines and so his faith weakened, grew cold and came into a dangerous state. As time went on he became more unduly critical and contentious. He was a quarrelsome man in his way and habits.
Mathesius, his pupil and first biographer says “As early as 1515 he was arleady called a heretic”. His rector, the famous Dr. Pollich said he had strange fancies and was disturbing orthodoxy at the universities. Luther called the theology being taught as “buffoonery”.
Juliusll wanted to restore the basilica of St. Peter which had fallen into decay, so he gave a lot of money and started the project but the funds eventually ran out. Leo the 10th, the successor of Julius decided to appeal to the Christian world and proclaimed a simple indulgence to all, wherever they may be, who would contribute according to their means for this holy project.
Leo 10th was acting in no way different from the practice of the Church before or since his time. The Pope has the right and privilege to grant and proclaim indulgences for charitable reason’s to help the building up of the Church. Special prayers, the visiting of a holy place within a certain time frame or as in this case the rebuilding of a basilica that was integral to Christian tradition and worship.
The person who was sent to preach on the indulgence came to Luther’s district and gave a talk at the university where Luther was a prof.Luther, already against the doctrine on indulgences did not like this very much and so he preached against this and said that remission of sin required nothing more than contrition and denied any satisfaction of forgiveness regarding the sacrament. He told everyone to disregard indulgences
and to give their money, not to the building of St. Peter’s but to the poor."(Smith
Luther and Tetzel, 20, 26).
Luther could not stand the fact that he wasn’t garanteed salvation.
He went to far, for the abuses of the clergy then, as they are visible to us today, are not a reason to start a new thing against the true thing. Luther’s attacks on indulgences (not beleiving the doctrine) were used as a cloak to conceal his own mad agenda. Did the Church need reforming? Doesn’t it always? Saint Francis and Catherine of Sienna helped the Church in this regard, they didn’t tear it asunder. Lutheran’s today have their own Bible because of Luther. He changed words to give credence to his Sola Fide idea and removed books to fit his fancies. Please see also,Galatians 1:8-9 / 2 John 1:9-11/ Acts 20:28-30 /
Peace and Love
I would like to see where the Pope has apologized to Luther and what the content was.

(See:
The Facts about Luther msgr. Patrick O’Hare,LL.D.)