How was Hamlet's conscience the main reason for delay when it came to killing Claudius?

In Act III, Scene 3, Hamlet has the chance to kill Claudius when he is all alone. However, Hamlet hesitates because Claudius is praying. He reasons that to kill Claudius in this way would only send him to Heaven. This is not the kind of revenge he has in mind. He notes that Claudius killed his own father in a much less devout state. The old King Hamlet was full of food and had his sins still on his soul ("his crimes broad blown"). Hamlet thinks it is more fitting to kill Claudius during a sinful moment. This seems to be a question of how his revenge will best be carried out. But it is a hesitation of Hamlet's conscience. It doesn't seem moral or fitting to kill Claudius during the act of praying. 

In the scene prior to this, Hamlet used the players to act out a scene in which a king is poisoned. Hamlet does this to get some reaction from Claudius because it mirrors his crime. Hamlet wants to see the guilt on Claudius's face. It is not enough to just kill Claudius. The death must be dramatized (pun intended). Ideally, he wants Claudius to be aware of his sin, mired in it, when he dies. It would only help the "state of Denmark" if that guilt is made public as well. Hamlet wants to wait for Claudius to be in particular inner (mental) and outer (public) states before he kills him. For Hamlet, ideally, Claudius will be spiritually and publicly guilty when he is killed. For Hamlet, this is about revenge as well as righting a spiritual imbalance left when his father was killed.