But ah! my foes and oh, my friends – (3)
The fact that our speaker addresses both her enemies and her friends is a pretty good indication of her own sense of self-worth. It's not often that you address both parties together (unless, of course, you're the President of the United States delivering the State of the Union address). And we're betting that the president has a healthy ego, as well. Linking friends and foes together suggests that our speaker wants everyone to bask in her glory.
lovely light (4)
How often would you describe yourself in absolutely positive, 100% glowing terms? Probably not too often. We're taught to be humble, to downplay our own successes instead of bragging about them. No one likes the kid who goes around talking about the number of free throws he just made or the number of medals she just won. Millay, however, doesn't suffer from such bashfulness. When she describes the light in the poem, it's unqualifiedly "lovely."
It will not last the night (2)
Even the brevity of the candle becomes part of its allure. By proclaiming the shortness of her candle's light, our speaker seems to be turning a bad thing (a dark night) into a source of pride. Brilliance, however brief, seems worth it to her—which makes it seem all the more appealing to us.