Why didnt Hamlet kill King Claudius when he sees him praying?

Answer 1

Because he thinks Claudius will go to Heaven if he kills him right then. As in many of Shakespeare's plays, the characters are Catholic, and believe that a person's fate in the afterlife depends on whether they get to confess their sins right before they die. Hamlet's father is in something like Purgatory because Claudius murdered him in his sleep, without getting a chance to confess. Hamlet feels it isn't true revenge if he sends Claudius to Heaven...he's really doing him a favor. He decides to wait and kill him right as he's committing some sin, to be sure he goes to Purgatory or Hell.

Ironically, Claudius feels he isn't able to successfully confess his sins, since he's not willing to make proper contrition by giving up the crown and his wife. If Claudius is right, Hamlet could still have sent him to Purgatory by killing him. Hamlet doesn't know this, so he misses his chance.

Curiously, according to Catholic theology, simply praying does not absolve you from the effects of the sins--that can only be done by a priest. (That is why they have confessionals--otherwise people would just pray and not bother going to confession) Therefore even if Claudius were praying it would not wipe clean any sins he had recently committed (including murdering his brother for which he surely had not received absolution from a priest). The idea that it might do so, and that Claudius can struggle with whether his prayer will work to do so are entirely Protestant ideas. Indeed, there is a struggle between Catholic and Protestant concepts in Claudius's soliloquy and in the play as a whole.