Lines 1-5 Summary

Get out the microscope, because we’re going through this poem line-by-line.

This alone is what I wish for you: knowledge.

Well, it looks like our speaker wishes someone else would get some sense.
From the title, we know who is doing the wishing. It's Demeter, goddess of agriculture. And she's talking to Hades, god of the underworld.
You see, Demeter's daughter Persephone was dragged down to the underworld by Hades, so she's understandably a little annoyed. Oh yeah, and we should add: Hades is Persephone's uncle. So… this is not exactly a match made in heaven, especially in a mother's eyes.
Demeter wants her back, and she's willing to do a lot to get her back.
Yeah, yeah, we know: another "beautiful princess gets captured and must be rescued" story. Anyone ever heard of Star Wars before? Of course, there's a reason myths are said to adhere to certain archetypes.
It's not all about the princess, though. Check out "What's Up With the Title?" for the whole (scandalous) myth.
Back to our first line: because Hades is god of the Underworld, the only way for Demeter to contact him is by praying to him. So that's just what she does.
And what does she wish for? Only one thing: knowledge.
Knowledge of what, we wonder. Let's read on to find out...

To understand each desire and its edge,

First of all, our speaker Demeter wants Hades to understand that the things he desires come at a price. That's the "edge." Dove creates an image here of something hard and sharp. Imagine running your hand along a smooth piece of paper… and then getting a paper cut—ouch.
This might sound vague, but Demeter's referring to Hades' snatching of her beautiful daughter. She's saying there will be a price—and it won't just be a paper cut—for Hades acting on that desire. That sounds like a threat to us.
Then again, Dove is being vague on purpose here. That's because, while this poem is ostensibly about a specific Greek myth, it's also full of feelings and situations we can apply to our own lives as reader.
Nothing comes for free, says our speaker. If you have a desire, consider all the consequences before acting on that desire. Otherwise—you'll need to keep the Band-Aids handy.

to know we are responsible for the lives
we change. No faith comes without cost,

Hades had a lot of power. After all, he is god of the Underworld.
As we all know, though, with great power comes great responsibility (or so say philosophers like Voltaire and Spider Man).
In this case, though, Hades took Persephone without considering what it would do to the lives involved. You see, according to the myth, when Persephone was taken to Hades, Demeter was so sad that she forbid anything from growing on the earth. Basically, it was endless winter (brrr). Of course, in winter, not much grows. So the food ran out, too.
Therefore, Hades' actions changed the lives of the mortals on earth quite a bit. As a god, he has that power, but he didn't use it responsibly. Way to go, Hades.
Now, Demeter tells him that he's responsible for the lives that he's changed. That's the price to pay when people have faith in you. At least, Demeter seems to think so.
Now that we are four lines in, does it seem like something is missing? Rhymes, maybe? Yep, this poem is written in free verse. Check out "Form and Meter" for more on what that's about.

no one believes without dying.

If we thought this poem was exclusively about some old Greek god-and-goddess drama, now we know Dove is saying something much more universal.
To have faith in something doesn't mean you've got a "get out of death free" card, she says. So it looks like faith has a two-way cost. The gods are become responsible for the lives that trust in them, but the believers also die—good times, gang.
And, by using an end stop (a.k.a. punctuation at the end of the line), she wants us to know that this is an important line, one that we should pause and consider.
Compare this end stop to the enjambment going on in the lines above. The sentences wrap around the poem, which means we keep reading without pause.
Check out "Form and Meter" for more poetic devices that make this deceptively-simple poem pack a subtle punch.