Right off the bat in the first line Milton uses a metaphor to compare his vision to a light source that could run out, like an old-fashioned lamp that burns through its oil. Later in line two, "Ere half my days", is a way of saying, "Before my life is through." But "days" also introduces the idea of daylight. The speaker's "days" are now more like nights. He uses another metaphor to compare his lack of vision to an imagined world that does not have light. The phrase "this dark world and wide" is also an example of alliteration. Then in line seven the speaker compares God – again using metaphor – to a master who makes his servants work in darkness. He "denies" them light, which sounds heartless. But then Milton goes into how he needs to be patient and listen to what God has planned for him.
Another element in the poem is the references to the Bible in different ways, like the word “talent” can mean either a sense of skill or money like what they used to use in Jesus’ time. In line one the word "spent" becomes a pun when we read it in a way of the discussion of money in the next few lines. The speaker's ability to see is like a currency, and he has unfortunately burned through it too soon.