Sneak peek means to preview something, like "I'll give you a sneak peek of the book!" Meaning, the person will give you a preview of the book (passages).
Explanation:
Mr.G said that, he is his father
You are Malvolio. Malvolio gets a letter from who he thinks is the wealthy countess Olivia, which suggests that she loves him. (It's a trick-people that he;s upset because of his snooty behavior have decided to spite him.)
So, t<span>he letter suggests that Olivia will show favour towards Malvolio and by doing that he will have greatness (high status) thrust upon him, and he is pleased to read this. </span>
