Duncan has never been to or seen Macbeth's castle before. He finds it very pleasant, which is ironic considering the fate that awaits him within. This deception of appearance is a good example of the theme the witches' established early on: Fair is foul and foul is fair. What looks so pretty and pleasant to the King is actually a death trap.

When talking about himself, Duncan uses the plural pronoun "we" in this section. This is known as the royal "we" and refers to a single person who holds a high office, such as a king or religious leader, and speaks for the well-being of many others.

Banquo is saying that even though there is no jutty (a projecting part of a building), frieze (a decorative band on an outside wall), or a coign of vantage (an advantageous position) the martlet likes Macbeth's castle so much that it has chosen to make its home (pendant bed) and nest (procreant cradle) there.

Martlets, or martins, are small birds related to swallows. Banquo indicates that this summer bird is attracted to Macbeth's castle and has chosen to make its nest on it. Banquo describes a quiet and idyllic summer day, which contrasts later with the storm that comes when Macbeth commits the foul deed.

It is interesting to note that King Duncan and Macbeth are never shown together after act I, scene IV. At the end of scene VI in act I, Duncan is being conducted to meet Macbeth, but in the next scene Macbeth is alone and plotting to murder the King. His wife comes in and says:

He hath almost supp'd. Why have you left the chamber?

So Macbeth and the King were eating and drinking together, but for some reason Shakespeare decided not to show them doing so. This may have been because Macbeth would have had to seem somewhat guilty and self-conscious—and Lady Macbeth does a much better job of deceiving their unsuspecting guest. To have had Macbeth do the same thing might have been redundant. Shakespeare seems to be trying to retain some degree of audience sympathy for Macbeth, because this is supposed to be his tragedy. Showing Macbeth being hypocritical with Duncan would be one way of losing some audience sympathy. It works better to have Lady Macbeth act out her own advice.

Duncan cleverly suggests that Macbeth was anxious to get home to his wife. Macbeth was digging his spurs into his horse's flanks to make it gallop faster. The King suggests that Macbeth was anxious to share a bed with his wife after a long absence from her and is probably still in bed!

In this short exchange, Duncan and Banquo speak to one another while approaching Macbeth's castle. Since performances of the play may not have had props or painted backdrops to represent the outside of a castle, Shakespeare typically relied on dialogue to establish time and place. In this instance, the stage directions only call for hautboys (woodwinds) and torches to help give the illusion that the characters are advancing to the castle.

This is ironic, of course, because Duncan does not know he is walking into a deathtrap. However the main purpose of his comments about the castle is to show that the King has never been here before, which means he is unlikely to come back again. He just happens to be staying with the Macbeths overnight because the fighting took place in this vicinity. Thus Macbeth has a one-time opportunity to murder Duncan tonight.

Lady Macbeth is being falsely polite. The language she carefully selects to welcome Duncan is obligatory. She must seem overly indulgent given Duncan's position as both king and as her husband's benefactor.