What is Act IV, Scene 1 in Macbeth about?

This scene is highly significant to the course of the play. In Act IV, Scene 1, Macbeth visits the witches again, seeking answers to pressing questions about his rise to power and his future. The witches, who open the scene (along with Hecate) by concocting a spell, answer him by summoning a series of visions. The first vision is an "Armed Head," which warns Macbeth to "Beware the Thane of Fife (Macduff.)" The next is a "bloody child," which informs Macbeth that "none of woman born" can harm him. A third apparition, which takes the form of a "Child Crowned, with a tree in his hand," reassures Macbeth that he cannot be defeated until Birnam Wood (a forest) marches against Dunsinane (Macbeth's palace.) In the final vision, Macbeth sees Banquo's image alongside eight kings, that are clearly intended to represent his heirs. Enraged by this, Macbeth demands that the witches answer his questions directly, but they depart, leaving him with his doubts. Macbeth decides to act on the visions, ordering the murder of Macduff's family--he learns from Lennox that Macduff has fled to England--and he is also emboldened by the second and the third visions. Yet the whole encounter leaves him questioning the motives and the trustworthiness of the witches. He exclaims "damn'd all those that trust them," a sentiment he repeats when he discovers, at the end of the play, that they have deceived him.