Final answer:
Macbeth's comment in line 59 is an understatement as it downplays his intentional role in King Duncan's murder, attributing it to being unprepared rather than his own ambition and moral choices. This serves to shift blame and seek sympathy, while the true nature of his action is far more malevolent and premeditated.
Step-by-step explanation:
The comment in question, "Being unprepared, Our will became the servant to defect; Which else should free have wrought." (l.59), is an understatement because it significantly downplays the severe consequences of Macbeth's actions.
The use of understatement here reflects Macbeth's attempt to rationalize and minimize the gravity of his involvement in King Duncan's murder. Macbeth suggests that had he been prepared, his will would not have succumbed to the 'defect' (the murder), an analysis that glaringly understates the active choice he made to kill the king.
This statement can be deceptive in its simplicity, as Macbeth shifts the blame to the circumstances, presenting his treacherous deed as almost an accident rather than the result of his own ambition and the manipulations by Lady Macbeth.
By faulting his unpreparedness rather than his character or moral decision-making, Macbeth is attempting to convey a sense of innocence, when in reality, his actions were calculated and deliberate.
By understating his role, Macbeth not only tries to avoid the weight of guilt but also seeks to gain sympathy from others, including the audience. This contrasts sharply with the true heinousness and premeditated nature of regicide, highlighting Macbeth's complex psychology and moral disintegration as the play unfolds.