50. Christians are to be taught that if the pope knew the exactions of the indulgence preachers, he would rather that the basilica of St. Peter were burned to ashes than built up with the skin, flesh, and bones of his sheep.
At the time of the writing of the 95 Theses Luther still had a belief in the good and holy intentions of the Pope. So in this Thesis he states that if the Pope knew what was being taught by the preachers of the indulgences he would be horrified and would stop that practice at once, since the building of the Cathedral was not worth the lives of his people.
The truth was that the Pope knew exactly what was being done with the sale of the indulgences. The system was devised so that with the sale of each indulgence, a portion went to the man who sold it, a portion went to the bishop of the region where it was sold, and the bulk of the money went to the Pope for the basilica.
In those days the Cathedrals would be built by the bishop or the Prince of the area. They built them for the people of their area to have a place to worship, but also they received all the funds that were donated there. So if they had relics (bones of the saints, etc.) for people to see and donate too they generated more money for the Prince or the bishop. If their Cathedral was bigger and fancier than the others in the area then more people donated there. The churches did not belong to the people or even to God, they were the property of the ones who built them.
In 1517 Luther did not yet understand that most of the people involved in the church trusted in their own works and their positions in the church rather than trusting in the mercy and love of God. They had all gotten side tracked with worldly thinking.
Dear God please forgive my stubborn reliance on my own works and the things of this world. Give me the support of Your Spirit that I may trust in You and live for you in all that I do. In Jesus name. Amen.