Okay kiddo, let me tell you about Matthew 21.
So, in the Bible, there is a book called Matthew and it talks about the life of Jesus. In chapter 21, Jesus comes to a town called Jerusalem and he tells his friends to go find a donkey and a colt.
He then rides on the donkey and the colt into Jerusalem, and there are a lot of people who are happy to see him. They think he is a king and they wave palm branches in the air and shout out "Hosanna!" This makes Jesus happy because he knows that they believe in him.
Jesus then goes to the temple - a big building where people would go to pray - and sees that there are people selling things inside. This makes him angry because he thinks the temple should be a place for prayer, not for selling things.
So, he starts tipping over tables and driving out the people who were selling things. He tells them that they are turning the temple into a "den of robbers" and that they need to leave.
After he does this, some religious leaders come to talk to him and ask him who gave him the authority to do these things. Jesus tells them a story about two sons, one who said he would do something but didn't, and the other who didn't want to do it but ended up doing it anyways. He says that the second son is like the people who believe in him, and the first son is like the religious leaders who say they believe in God but don't really follow his teachings.
So, that's a little bit about Matthew 21. Did that make sense to you, kiddo?