It was to convey a sense of fate and superstition, which the author wanted to intent showing Macbeth’s persona and fate later on the play, establishing a inquisitive atmosphere for the reader, hooking them in and wanting to know the fate of Macbeth at the end of the play.
He does not like his grandmother to talk about his new school because he is embarrassed that the teacher was sucking up to him. He was bothered by the special treatment because he thinks its embarrassing