In Stave 2, before the first spirit arrives, Scrooge's attitude is dismissive of the whole situation. He refuses to believe that Marley's ghost was real and keeps insisting it must have been a dream. He is more annoyed by the intrusion than anything.
"Marley's Ghost bothered him exceedingly. Every time he resolved within himself, after mature inquiry, that it was all a dream, his mind flew back again, like a strong spring released, to its first position, and presented the same problem to be worked all through, 'Was it a dream or not? "(Dickens)
By the time he is visited in Stave 3, by the second spirit, his attitude is dramatically changed. His tone of disbelief and irritation is replaced with one of fear and anxiety with the thought of what the next spirit might be like. He no longer thinks that he is dreaming; the experience is very real to him. In fact Scrooge is ready to face the spirit because he wants to confront it so that it does not sneak up on him.
"For, he wished to challenge the Spirit on the moment of its appearance, and did not wish to be taken by surprise, and made nervous." (Dickens)
Now, he is ready for anything, realizing that anything is possible and that his lack of belief was misplaced.
"Now, being prepared for almost anything, he was not by any means prepared for nothing; and, consequently, when the Bell struck One, and no shape appeared, he was taken with a violent fit of trembling." (Dickens)
He is definitely intimidated by the anticipation of waiting for the next spirit. He is humbled by the fact that he has no control over where the spirit will appear, or in what form, and this makes him uncomfortable. But when he encounters the Ghost of Christmas Present, he is roundly welcomed by the jovial spirit who has transformed a room in his home into an abundant expression of the bounty of Christmas.