Hamlet is going to see his mother now. I am going to hide and spy on him.
The King's Regret
I feel such regret! I should not have poisoned my brother just for materialistic means!
Hamlet's Attempt at Revenge
I cannot kill him while he is praying or else I will not get full revenge for my father. I must kill him when he is sinning and drunk.
Polonius is telling King Claudius that he will go and spy on the conversation he thinks Hamlet will have with his mother, not knowing that Hamlet is actually coming to the King's room.
King Claudius is feeling very regretful for murdering King Hamlet and is now praying and repenting.
Hamlet runs to Claudius' room with a sword. He wants to kill Claudius but realizes if he murders him while he is praying, he will go to heaven. Hamlet then decides to kill him another time while he is sinning to get full revenge.