From the get-go, we can tell that this is going to be a poem about writing poems. In most other poems you read, the poet’s just going to go ahead and tell you what he wants to tell you, but here the speaker feels compelled to ask if he should go ahead with the whole thing. It’s almost as if he’s including the beloved and (since we read the poem) the audience in the construction of the poem, asking for our input. Then, of course, there’s the fact that this is an empty offer of a question – neither the beloved nor we in the audience can possibly change the course of the poem, and we might even see this opening line as a bit of arrogance.
Nor shall death brag thou wander’st in his shade, When in eternal lines to time thou grow’st (11-12)
Here’s where the poem starts to move into more meta territory, bringing out that central issue of immortality through artistic representation. First we get to see a real-life example of artistic immortality, as lots of readers will recognize the "death" through whose "shade" we wander from another famous work of literature: the Bible (and specifically Psalm 23:4). Here’s a character who seems to have gained some literary immortality, since so many people read the Bible. Then the speaker gets even more assertive, contending that the beloved will "grow" in "eternal lines to time." That phrase "lines to time" is definitely a description of poetry, since poems are lines of words set to a rhythm, or time, so the poet’s pointing toward eternal life through poetry.
So long as men can breathe, or eyes can see, So long lives this, and this gives life to thee. (13-14)
Well, these are some of the most famous lines in all of Shakespeare, and for good reason. Here’s the poet’s deserved arrogance in all of its glory: as long as people keep reading, this poem will stay alive, and, in turn, so will the object of the poem, the beloved. Note here he makes the tacit assumption that as long as people are reading, they’ll be reading his poem. Cocky stuff.