This was another one that I just happened to flip to and it confused me a bit. Here's what I've managed to pull from it so far. I'll need some help on this one. The last two lines seem pretty clear in meaning.
True eloquence occurs through silence.
Because the workings of our minds are so complex, sometimes our voices don't do our minds justice. But maybe she's also touching on relationships and how wonderful ui can be for two people to be able to communicate silently. I wondered, too, what the first two lines were about, when first I read this poem. This seems to indicate that Emily has sometimes taken silence for refusal, or denial, at least as something negative. This poem could be interpreted as Emily evaluation of other's responses.