What does 1 Samuel 2:25 mean?

'If someone sins against another person, God can step in as a mediator. But if you sin against God Himself, who's going to speak up for you?' But his sons wouldn't listen to their father, because God had already decided to bring them down. 1 Samuel 2:25 - Modern Text Bible

(Eli warns them that their sins are especially serious because they're against God, but his sons ignore him. Their fate is already sealed.)