WHY DOES MACBETH DECIDE TO KILL MACDUFF'S FAMILY?

The witches circle a cauldron, mixing in a variety of grotesque ingredients while chanting "double, double toil and trouble; / Fire burn, and cauldron bubble" (10-11). Hecate appears, they sing all together, and Hecate leaves. Macbeth then enters, demanding answers to his pressing questions about the future. The witches complete their magic spell and summon forth a series of apparitions. The first is an armed head that warns Macbeth to beware the Thane of Fife (Macduff).