Macbeth and Banquo see Ross & Angus, who bring news of honours to Macbeth. This is the event that will cause Macbeth to begin thinking about killing King Duncan.
The former Thane of Cawdor betrayed Scotland, and the king says you're very brave and noble, Macbeth!
Hey Macbeth, the king told us to tell you that you're the Thane of Cawdor now!
Whaaaaat? The strange beings were right!
Macbeth begins to think about the events which have just occurred, and what they mean for the future. This is where he begins to truly consider the treasonous and ambition-driven plan, which he and his wife will attempt in the future.
Macbeth, I wouldn't trust those strange beings. They may just be trying to gain your trust, which they will later use to their advantage. Now, let's head home. I'm ready when you are.
So, the witches' first prediction was right... I wonder if fate will make me King, or if I must do something to make it happen. I now find myself thinking of killing King Duncan to make myself King... no, that's a terrible, awful thought... right?