Well kiddo, there are some people in this world who don't believe in Jesus. That means they don't think he's a special person who came to Earth to save us. They might think he was just a regular guy or maybe they don't believe he existed at all!
When someone rejects Jesus, it means they are saying "no thank you" to his teachings and his love. It's like when your friends invite you to play a game and you say "I don't want to."
Now, some people have many different reasons for rejecting Jesus. Maybe they follow a different religion, or maybe they just don't believe in any religion at all. It's important to remember that everyone has their own beliefs and opinions, and we should respect them even if we don't agree.
The most important thing is that we love and care for each other, even if we don't have the same beliefs. So even if someone rejects Jesus, we can still be kind and compassionate towards them, just like Jesus would want us to be.