The first words we hear from Macbeth are echoes of the witches’ last words in scene 1. What significance is there in this coincidence?

At the end of act 1, scene 1, the Weird Sisters speak the words,

Fair is foul, and foul is fair;Hover through the fog and filthy air (1.1.12-13).

This appears to mean that, from here on out, what seems good can actually be bad and what seems bad can actually be good. In short, appearances can be deceiving (a major theme of the play). When we first hear from Macbeth, he is on his way home from a terrible double-battle against the forces of a Scottish rebel as well as the forces sent by the Norwegian king. Macbeth says to his friend and comrade, Banquo, "So foul and fair a day I have not seen" (1.3.39). This seems to refer to the battles. War is violent and foul, but Duncan's army, led by Macbeth and Banquo, has claimed victory, and this makes the day fair. It might seem foul because so many men have died, but loyalist forces have won. Macbeth's repetition of the words "foul and fair" let the audience know, early on, that this is going to be an important motif throughout the play and that we should listen carefully for further references to it.