I'll make so bold to call, / For 'tis my service" (Shakespeare 2.3.64-65)
"They were all struck for thee! naught that I am, / Not for their own demerits, but for mine" (Shakespeare 4.3.266-267)
Bring thou this fiend of Scotland and myself; / Within my sword's length set him" (Shakespeare 4.3.274-275)
When Macduff is introduced, he is shown to be very loyal to King Duncan, serving him with whatever he needs and making sure to fulfill his duties. Macduff is polite and glad about his job, content with being of service to the king.
Macduff has become flooded with grief when he discovers that his family is murdered. Immediately, he begins to blame himself and his disappearance for the cause of this. He cries that his family is innocent and that it was his actions that allowed this to occur.
Macduff is encouraged to turn his grief into anger towards Macbeth. Immediately, he plots to kill Macbeth and end his reign of terror. He no longer has mercy for the traitor and has decided to fully take matters into his own hands.