Banquo's short soliloquy has two purposes: It reminds the audience of the details of the Witches' prophecy in Act I, and it reveals his own suspicion that Macbeth is Duncan's murderer. Ironically, his tone also recalls the ambitious tone of Macbeth in earlier scenes.
Macbeth and his wife make arrangements for the feast with all the confidence of their new rank. Note particularly Macbeth's adoption of the royal "we," The use of the plural in place of the singular pronoun is a traditional figure of speech by which the monarch expresses not only unity with his people but also his absolute authority over them. Banquo, once equal in status with Macbeth, acknowledges Macbeth's new position by addressing him throughout the scene as "my lord."
Other aspects of language confirm Macbeth's new status: strong verse rhythms, for example, appear in lines such as "Here's our chief guest" and "Fail not our feast." Macbeth's apparent disregard for time — of which he now has plenty — is clear in expressions such as "but we'll take tomorrow" and "But of that tomorrow." The word "tomorrow," like "hereafter," is full of irony in Macbeth. Tomorrow should be full of hope for the future, but the word comes back to haunt him later in the play. His use of the word here foreshadows the famous "Tomorrow and tomorrow" speech in Act V.
