What is the significance of Duncan entering in Inverness in Act 2 prior to the murder scene of Macbeth?
Concerning Duncan's arrival at Inverness in Shakespeare's Macbeth, he actually enters in Act I:6. There are a couple of important aspects of his arrival beside the fact that it gives the Macbeths a great opportunity to assassinate him.
First, his arrival provides dramatic irony when he and Banquo talk about the castle as they approach it. They use words like pleasant and delicate to describe the castle and the air around it. They don't know that the Macbeths are inside of the castle plotting Duncan's destruction. Since the audience does, the scene provides dramatic irony.
Once inside, Duncan greets Lady Macbeth with kind words and much respect. She is "our honored hostess" and he even apologizes for putting her to so much trouble.
This, too, is ironical because Lady Macbeth will play a major role in killing him before the next sunrise, and because receiving Duncan is no trouble at all for Lady Macbeth, she is tremendously excited to have her victim in her house.
The contrast between good and evil is also highlighted by Duncan's arrival. Duncan is good, and Lady Macbeth is evil.