Duncan has just appeared at the castle. Lady Macbeth is greeting him and offering him a (false) hospitality, as she has just plotted his murder. Duncan says that he had hoped to arrive before the Thane of Cawdor, an allusion to Macbeth's new title, but that Macbeth, riding fast, got home faster. Duncan ends by saying he is her guest for the night.

Speaking formally, Lady Macbeth says that all that they have is in compt, or obligation to the king and that he can inspect or examine it all as he wishes. It is all the king's.

This scene is filled with dramatic irony: Duncan does not in the least suspect what the audience already knows, that the Macbeths plan to murder Duncan. What Lady Macbeth is saying is that all that is here might belong to the king, but Duncan, though he does not know it, will not be king for long. Accounts are very much going to work out in favor of the Macbeths, she thinks.

Lady Macbeth is already planning the murder of Duncan by Act 1 Scene 6. The extended financial metaphor would, on the surface, be a way of interacting in a witty but respectful way with her esteemed guest, the King. However, as we also appreciate the duplicity of Lady Macbeth, and her vile motives, it is possible that her words also have a more sinister suggestion.

My interpretation would be that Lady Macbeth is considering the ideas of ’worth’ and ‘value’. Her husband has risked his life for his monarch, and will be financially rewarded for his efforts, but she sees a greater value in the power that he could be afforded had he dispatched the king himself, rather than his enemies. As the witches’ prophesy adds weight to her contemplations, by Act 1 Scene 6 she is considering the debt that her husband is owed, and how Duncan should pay with his life, rather than his gold.