How does Macbeth react to Macduff at first?

At first, Macbeth underestimates Macduff and dismisses him as a threat. He says, "The castle's strongly fortified, and we / Resolve to meet in the field" (Act 5, Scene 5). Macbeth believes that his power and the strength of his castle make him invincible. He does not consider Macduff to be a serious opponent and is confident that he will be able to defeat him easily.