In John 13, there's a story about Jesus and his disciples. They were having a meal together and they were all sitting at a big table. Jesus noticed that nobody had washed their feet, which was a custom in those days. So, he got up from the table, took off his robe, and put a towel around his waist.
Then, he took a bowl of water and started washing his disciples' feet one by one. The disciples were really surprised by this because they thought it was a servant's job to do that. But Jesus explained that he was doing this as an example of how they should treat each other - with humility and service.
While he was washing their feet, he came to Peter, who didn't want Jesus to wash his feet. But Jesus explained that if he didn't wash his feet, then he couldn't be a part of what Jesus was doing. So, Peter let Jesus wash his feet and he felt really humbled by Jesus' love and service.
After he finished washing everyone's feet, Jesus put his robe back on and sat down at the table. He explained to his disciples that whoever serves others is the greatest in the kingdom of heaven. And he also told them that one of them would betray him. This made the disciples really sad and they asked who it was. Jesus said it was the one who he gave a piece of bread to. And when he gave it to Judas Iscariot, he left to betray Jesus.
So, John 13 is a story about love, humility, and service. Jesus showed his disciples that if they want to be great, they need to serve others with love and humility. And he also warned them about the betrayal that would soon happen.