Hello. You did not enter the text to which these questions refer, which makes it impossible for them to be answered. However, I will try to help you in the best way possible.
1. The main purpose of the speaker when addressing "you" in the poem is to establish direct communication with the reader. This makes the reader an element of the text and can interact with everything that is being exposed in the poem, thus becoming a confidant of the speaker and part of the text.
2. If the speaker's point of view was changed, the reader would no longer be part of the poem, but would be someone who has a view of the poem from the outside, without having to get involved in anything the speaker is exposing. This leaves the reader as a more superficial participant.