What discussion of gender roles emerges in Act IV, Scene 3?
The Macduffs are foils of the Macbeths, though in Act IV scene ii it seems that Macduff makes the same mistake that Macbeth makes in Act III, which is failing to consult with his wife and placing matters of the state above matters of the family.
Macduff, though absent in the scene, will discuss manhood in the next scene, iii. Regarding the murder of his family, Malcolm will say to Macduff:
Dispute it like a man.
Macduff will answer:
I shall do so, / But I must also feel it as a man.
Macduff is sensitive to the murder of his family, unlike Macbeth, who defines manhood with murder. But, Lady Macduff begs the question: why forsake the family for the state in the first place?
To understand this, one must understand "comitatus," the King-Thane relationship. Macduff, a thane, is bound to serve his king by protecting his land and life. If the king is killed, the thane is bound to avenge the king's death. So, Macduff is off seeking revenge against Macbeth, while Macbeth, not bound to any loyalties, is seeking murder against all the Macduffs to pre-empt the witches' prophecies.
Lady Macduff, who is bound to the family, cannot understand these male bonds of revenge. It's all traitorous murder in her eyes. Lady Macduff cannot understand why a man (Macbeth) would murder her and her son, since there is no political reason to do so. Lady Macduff cannot understand why her husband would leave her defenseless. She says to Ross:
Lady Macduff's monologue reveals the key gender differences:
Wisdom! to leave his wife, to leave his babes,
His mansion and his titles in a place
From whence himself does fly? He loves us not;
He wants the natural touch: for the poor wren,
The most diminutive of birds, will fight,
Her young ones in her nest, against the owl.
All is the fear and nothing is the love;
As little is the wisdom, where the flight
So runs against all reason.
A mother would never leave her babes. Macduff's flight is neither wisdom, nor fear, nor reason. She calls it traitorous (to the family), whereas Macduff might answer that he is defending country above family. It's all a matter of priorities.