Act 4.3 is the longest scene in Macbeth and seems to abruptly halt the dramatic flow of the play. We have seen fast-paced murder and await revelation and retribution. It comes, but only after 150 lines of dialogue in which Malcolm seems to equivocate to Macduff, as a test of his loyalty.
A tricky scene. Useful because we see an alliance being formed and can focus on the negatives of Macbeth when seen in contrast to Malcolm, and, most importantly to Edward. His saintliness allows Shakespeare to make a clear alignment of Good VS Evil as we enter Act 5.
English Teaching Resources 
[…] The long dialogue between Malcom and Macduff is unexpected and this whole scene rather slows the progress of the play. A teaching slide-deck can be found here: Act 4.3 A scene of Mirrors. Macbeth. […]