What is the dramatic irony of Hamlet’s choice to sheath his sword and forestall revenge against Claudius in Act III, Scene iii?
Claudius is suicidal, and rather than praying for forgiveness, he is actually praying for someone to kill him and end his misery.
Claudius is plotting Hamlet’s downfall even as Hamlet refrains from assuring Claudius’s end. While he looks as if he is praying, he is articulating a clever scheme for Hamlet’s murder.
Hamlet’s sword has come into contact with poison, so he would only need to scratch Claudius to kill him. However, Hamlet doesn’t know this and only hesitates because he isn’t prepared to run Claudius through with his sword.
Hamlet won’t kill Claudius because Claudius appears to be confessing and Hamlet frets that his soul will ascend to heaven, but actually, Claudius has not confessed anything and would therefore have no assured path to heaven.
Claudius considered killing King Hamlet in much the same fashion as Hamlet considers killing Claudius, but Claudius sheathed his sword as well, opting instead for ear poison.