Lady Macbeth's False Hospitality
Lady Macbeth enters and puts on the performance of her life, playing the perfect, gracious hostess. She speaks in flowery, elaborate language about how honoured they are to have the king stay with them.
Duncan asks where Macbeth is, explaining that they tried to catch up with him on the road but he rode ahead. The king praises Macbeth's loyalty and says how much he values him as a subject.
Lady Macbeth continues her act, telling Duncan that everything they own belongs to him as their king. Duncan is completely charmed by her hospitality and asks her to lead him to Macbeth.
Remember: Lady Macbeth's polite, respectful behaviour is a complete mask. Just one scene ago, she was planning Duncan's murder and calling on evil spirits to fill her with cruelty.
The scene ends with Duncan following Lady Macbeth into the castle - essentially walking to his death whilst thanking his future murderers for their kindness.