Martin Luther was a university student, studying law. He studied law in hopes of being a lawyer, with his dad being a miner to pay for his tuition.
One day, Luther was caught in a storm with lightning flashing everywhere. He thought he was going to die. So, he prayed to God to be spared and said he would be a devoted Christian if he's spared.
Save your salvation with an indulgence.
And so, he lived to see another day. He became a devoted Christian. He attended Church every Sunday and Holy Day Obligations. He eventually had to drop going to school in exchange for attending church.
One day, Luther decided to move to Rome to continue in his faith and it was sort of a pilgrimage to him.
While at Rome, Luther decided to visit Saint Peter's Basilica. At the Basilica, he saw someone selling indulgences. What they basically were was a piece of paper that would give you salvation. But, you had to pay the church to own one and Luther knew that these things weren't legit.
So for hours on end, Luther studied the bible. This made him question his faith in the Catholic Church because of how many teachings went against the bible.