Okay kiddo, so a long time ago, people believed in a religion called Christianity, but they had different ideas about how God decides who gets to go to Heaven. These two groups were called Calvinists and Arminians.
Calvinists believed that God already knew before you were born if you were going to go to Heaven or Hell, and there was nothing you could do to change it. Arminians, on the other hand, believed that everyone had a choice in whether they went to Heaven or Hell, and that by believing and having faith in God, you could choose to go to Heaven.
These two groups didn't agree on this, and they argued a lot. Some people thought Calvinists were too strict and scary, and some people thought that Arminians were too loose with their beliefs and not serious enough about faith.
Even today, people still have different ideas about this, but it's important to remember that no matter what you believe, it's important to treat everyone with kindness and respect.