He is contemplating the murder of Julius Caesar. He says:
It must be by his death: and, for my part,
I know no personal cause to spurn at him,
But for the general. He would be crown'd:
How that might change his nature, there's the > question:/
He is thinking and pondering about murdering Julius Caesar, thinking that he has to die as he knows that Caesar was going to be crowned king over Rome. He felt that Caesar might be politically-corrupted by his power after rising up to the throne. He felt that if he need to quash his lingering doubts, he had to kill him.