How we cite our quotes: (line)
Quote #1
When I consider how my light is spent, (line 1)
The speaker's guilty thoughts start with consideration of his blindness. You get the feeling that he has had these thoughts before, and maybe even often. Does he blame himself for his lack of "light"?
Quote #2
Ere half my days (line 2)
How does he know how many days he has left? Isn't it presumptuous of him to say how long he "should" live? If you're a Christian like Milton, then God decides how long you live. Clearly, he is looking for some kind of meaning in or justification of his blindness.
Quote #3
and present
My true account, lest he returning chide; (lines 5-6)
According to the Christian religion, on the Day of Judgment, or at the end of his life, the speaker will have to relate how he has spent the time that was given to him on earth. He worries that God will "chide" or blame him for using the "currency" of his talents unwisely.