why dose hamlet not kill the king when he finds himm praying? what is ironic about this inaction?

Hamlet thinks that killing Claudius during prayer would do Claudius a favor. Unlike Hamlet's father, Claudius is purging his sins to God and would be sent to Heaven. Hamlet wants revenge when Claudius is in the middle of his many sins. The irony is that Claudius cannot pray and repent to God. He is not sorry for his sins and wants to keep everything that he sinned for.