Imagine that your younger sister has decided that she wants to buy a new doll, but your parents will not give her the money. She decides to run a lemonade stand so that she can earn enough to get the doll. Your parents agree, as long as she puts half the money that she earns into a savings account.
For the first few days, the lemonade stand works really well! Everyone in the neighborhood stops by to get some delicious lemonade, especially because it's the summer and it's been really hot for weeks. Soon your sister has enough money to get the doll that she wanted, but she doesn't stop there.
Because the lemonade stand worked so well, she decides to keep running it to make more money for toys. You're starting to get worried. Your sister is beginning to cheat some of her customers, like the rich old lady who lives down the street, by charging them extra. She's also giving special favors to her friends, like free lemonade. Worst of all, she's lying to your parents about how much money she is earning, so she doesn't have to put as much into her savings account.
In the sixteenth century, the Catholic Church was becoming just like your sister's lemonade stand -- they were not keeping their promises. One man started to notice the things wrong with the Church. He noticed that they were giving favors to people who were rich. He noticed that they were spending money on selfish things instead of giving it to the poor. Martin Luther was the name of the man who started a movement to change the problems he saw in the Catholic Church.
When you noticed the problems with your sister's lemonade stand, you knew you had to be very careful about how you pointed them out, otherwise your parents would think you were tattling. You might even get in trouble instead of her! So you spent a few days taking notes on the things she was doing wrong, and decided to make a list of complaints to show your parents. This way they were much more likely to believe you.
Martin Luther did almost the same thing with the Church. If he ran around telling everyone what was happening, they might think he was not telling the truth, or that he did not know what he was talking about. He might even get in trouble. So Martin planned what he wanted to say very carefully, and he also made a list of all the problems he was seeing. The 95 Theses was a list of all the questions and ideas Martin Luther had to change the church.
Imagine that you wanted everyone in your neighborhood to know about the problems with your sister's lemonade stand, not just your parents. You would have to find some way to make copies of your list. You didn't want to write them all out by hand, because that would take way too much time. Eventually, you went to the copy store and made hundreds of copies. Now you can pass them out to all your neighbors.
Martin had the same problem hundreds of years ago, but they did not have copiers back then. In fact, if you wanted a copy of something written, the only way you could get it was to write it by hand. That would be like you writing out the list hundreds or maybe even thousands of times! Martin got really lucky, though. Right around the time he was criticizing the church, there was a new invention that helped him a lot. The printing press was a machine that allowed people to make many copies of things without writing them by hand.
Using the printing press, Martin made copies of his 95 Theses. Soon, everyone had seen them! Some people were really angry that Martin was saying bad things about the Church and wanted things to stay the same. Others started to pay attention to the problems that had been there all along. People got angry and decided to deal with it in different ways. Some people protested against the Church, while others decided to start new churches. The Protestant Reformation was the name of the movement that broke away from the Catholic Church to start new religions that would fix many of the problems they saw in the Catholic Church's beliefs and practices.
Just like passing out the list of what your sister was doing wrong would help make the neighborhood better, Martin Luther's list also made the Catholic Church better. Your parents would make your sister fix her lemonade stand, just like the church fixed itself. Also, your neighbors may start going to a different lemonade stand because they do not trust your sister any more, just like some people founded their own churches. Either way, Martin Luther's 95 Theses made a huge difference in the history of Christianity.
References:
KDG Wittenberg. "The 95 Theses" luther.de, 1997.
<http://www.luther.de/en/95thesen.html>
Linder, Douglas O. "The Trial of
Martin Luther: An Account" law2.umkc.edu, 2010.
<http://law2.umkc.edu/faculty/projects/ftrials/luther/lutheraccount.html>