In the cave of the witches the cauldron is boiling, and Macbeth comes to get answers to his questions. Only we never hear his questions, as it is said that the apparitions know his thoughts. He again gets three predictions. An armed Head tells him to beware Macduff, a bloody Child - to be bloody and resolute, as "none of woman born shall harm Macbeth", and a Child crowned with a tree in his head prophesies, that "Macbeth shall never vanquish'd be until Great Birnam wood to high Dunsinane hill shall come against him". This reassures Macbeth, but something else tortures him - he wants to know if "Banquo's issue ever reign this kingdom". Now, why does this trouble him so much? I guess it is the issue of fertility here - Macbeth has no children, and that's what really troubles him. Anyway, witches show him the line of kings of Banquo's blood. Macbeth is in rage, and when a messenger comes to tell him that Macduff has gone to England, he decides to "surprise" his castle and kill his wife and children. (Seriously, I think he really has some complex about not having children, if he wants to kill everybody else's)
In Macduff's castle his wife is worried that her husband has left them, but still hopes that nobody will touch he and her children, as they haven't done anything. Of course, this didn't convince the killers sent by Macbeth. She and all her children are killed.
The war is coming. Macduff has found Malcolm in England, and they arrived to the decision to go to war for Scotland. When Ross comes with news of the slaughter of Macduff's family, they are even more determined. Moreover, England is ready to give some thousands for their cause.
What I like most in this scene is the description of the state of affairs in Scotland, as seen by a patriot:
Alas, poor country!How much sorrow is there in those lines! Can't it be applied to some countries today? Yes, it can. And I'm not even pointing at the one in particular. At least not explicitly.
Almost afraid to know itself. It cannot
Be call’d our mother, but our grave; where nothing,
But who knows nothing, is once seen to smile;
Where sighs and groans and shrieks that rend the air
Are made, not mark’d; where violent sorrow seems
A modern ecstasy; the dead man’s knell
Is there scarce ask’d for who; and good men’s lives
Expire before the flowers in their caps,
Dying or ere they sicken.