Duncan's words in this scene establish not only his trusting nature, but also the lengths to which Duncan's goodness extends. The scene occurs after his forces had to suppress a rebellion by the traitorous ex-Thane of Cawdor, and here Duncan arrives at the castle of Macbeth, the new Thane of Cawdor, who is also having treacherous thoughts. Yet Duncan believes nothing but the best is possible from Macbeth, Lady Macbeth, and their home.
Duncan's first comment regarding the atmosphere of the castle itself is a strong example of dramatic irony, given what will occur later, but it also connects Duncan's belief of the goodness of the castle to the greater world. The castle "hath a pleasant seat," but also "the air / Nimbly and sweetly recommends itself / Unto our gentle senses" (1-3). In other words, nature approves of the castle. Banquo extends this connection, mentioning how the martlet has built a nest and, despite the fact that there's really no good place to see exactly what is happening at all times, the bird's choice of Macbeth's castle does show that nature approves of the abode. This also lends itself to the forthcoming murder of Duncan as a crime against nature, because Macbeth's actions betray both the king and the natural world.
When Lady Macbeth enters, Duncan's words again reveal his inability to suspect Macbeth. He greets Lady Macbeth with his love, and then inquires about Macbeth's whereabouts, stating:
We coursed him at the heels and had a purpose
To be his purveyor; but he rides well,
And his great love, sharp as his spur, hath helped
To his home before us. (26-29)
Here Duncan shows his inability to even fathom that Macbeth is up to no good. Clearly Macbeth rushed home to discuss this situation with his wife, yet Duncan believes that Macbeth rushed home because he loves his wife so much. In Duncan's mind, Macbeth's hurry was due to his love, not his desire to make plans for the king's demise.
The scene ends with Duncan's continued graciousness toward his hosts, and since this is the last scene in which the viewer sees Duncan alive, it leaves a lasting impression of his pure, innocent, trusting nature. This, in turn, makes Macbeth's ability to kill Duncan even more terrible, and turns Macbeth into even more of a villain.
In this scene, King Duncan and Banquo arrive at Macbeth's castle where they will stay the night. Duncan's words throughout the scene show his gracious, trusting nature. When he first sees the castle, he comments upon its pleasing location and the soothing sweetness of the air. These comments develop a strong dramatic irony, since we know this is the place where Duncan will die. The dramatic irony is further developed when Duncan goes inside and meets Lady Macbeth. He greets her with warmth and affection and thanks her for her efforts to host his visit. He also expresses his love for Macbeth and his intention to "continue our graces toward him." Duncan's remarks and his demeanor develop his character as a kind and grateful ruler, thus heightening the horror of his impending death.