Okay kiddo, so a long time ago, there was a man named Martin Luther. He was a really important guy who did some stuff that changed the way people think and believe about religion. One of the important things he did was make a list of books that he thought should be part of the Bible, and another list of books that he thought should not be in the Bible. This list is called "Luther's Canon."
Now, the Bible is a big book made up of lots of smaller books, and some people think that all of the books in the Bible are equally important and should be included. But Martin Luther didn't think that. He believed that some of the books didn't belong in the Bible because they didn't really belong to the original scriptures.
So, Luther put some books in his list, like the books of Genesis, Matthew, Corinthians and others. But he also left out a few books like Tobit, Judith, Sirach, Baruch, and 1 and 2 Maccabees.
While some people agreed with Luther's decisions, others didn't. This made some people upset but it also inspired more debates and discussions among people. But that's okay, because everyone has their own opinion and it's important to be able to talk about it, even if we don't agree with each other.