This quotation encapsulates Hamlet's dilemma in a nutshell. On the one hand, he wants to exact a bloody, terrible revenge on all those who've wronged him—especially Claudius, the man who murdered his father. Deep down, he often wishes he could be like the tyrannical Roman Emperor Nero, a man renowned for his cruelty.
On the other hand, Hamlet still takes the ideal of a Christian prince seriously enough to pull back from the brink and not let his desire for revenge consume him to the point where he becomes someone and something he isn't.
To a large extent, it's Hamlet's desire to avoid becoming another Nero that is responsible for his notorious procrastination. Instead of dashing off to the palace and killing Claudius when he finds out he was responsible for murdering his father, he bides his time for what seems like an eternity. And this is mainly because he doesn't want to be seen as a cruel and vicious tyrant like Nero.