Stanza 3 Summary

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

--My friend, I want to trade
my horse for her house,
my saddle for her mirror,
my knife for her blanket.

In this section, a dialogue begins. Here, the speaker is talking to a friend. What's he saying?
It's time for Let's Make a Deal! Yes, that game show you all (or maybe just some of you older folks) know and love is back, with fabulous prizes and oddly dressed contestants! Our speaker is playing today, and he'd like to trade a horse, a saddle, and a knife! In exchange, he's hoping to get the green girl's house, her mirror, and her blanket. Awesome swap?
What's telling about these lines is the nature of the things the speaker wants to trade (horse, saddle, and knife), and the nature of the things he wants (house, mirror, blanket). It seems like he wants to get rid of things associated with traveling and roaming (a horse and saddle), as well as maybe violence or fighting (a knife). And now he's after some peace and security (a house and a blanket), as well as a way to check out his new haircut (the mirror).
Actually, the mirror would allow the speaker to see himself clearly. It's as though he wants to change his mode of life here. The green girl and her possessions seem to be the key to that change.

My friend, I come bleeding
from the gates of Cabra.

Ouch. Here's a history and geography tidbit for you: Cabra is a village in southern Spain, where Lorca lived. One thing to know about the history of Spain, and southern Spain in particular, is that it was at one time (from 711-1492) under the control of a group of north African, Islamic rulers called the Moors. In 1492, something called La Reconquista (the Reconquest) was completed, in which Catholic armies kicked out the Moors (and the Jews) for good, after a long, bloody struggle. (For more on the Reconquest and Islamic Spain, check this out.)
Cabra was a village that was involved in that violent war, and here the speaker hints that he's been wounded in, or by, this conflict.

--If it were possible, my boy,
I'd help you fix that trade.
But now I am not I,
nor is my house now my house.

Some friend. The person in the other part of this dialogue is unable to help make the deal happen. Bummer. He's (again, we use "he" generically) got some odd reasons for not being able to help, too. He's just not himself, it seems. But we don't see it as though he's just having a bad day. It's as though the speaker's buddy is literally not the person he thought he was. And his house? Yeah, that's not his house either. Everything that was intimately familiar to him—even his own sense of self—is now somehow strange. It would seem that the speaker is not the only person in need here. While he longs for a girl, and a life, that he cannot have, his friend suffers from an even more fundamental kind of estrangement. Yikes. Things are getting serious.

--My friend, I want to die
decently in my bed.
Of iron, if that's possible,
with blankets of fine chambray.

Okay, then, how about this? Here we get the speaker's counter-offer. If he can't work a trade for the green girl's items, then maybe, just maybe, he can die in his own bed. That's a pretty lame consolation prize, but the speaker wants it nonetheless.
Hey, at least the bed sounds nice. Iron railings? Fine blankets? (Chambray is a lightweight, delicate fabric.) We can think of a lot worse places in which to die.

Don't you see the wound I have
from my chest up to my throat?

But why does the speaker want to die at all? Oh, right. We almost forgot—he's been wounded. It sounds bad. Can't his friend see that giant wound in the speaker's chest?
Hmm. Tellingly, his wound seems to be over his heart. In fact, it's definitely more than just a random injury. Our speaker seems fundamentally damaged at the core of his being. Sadly, that sounds fatal.

--Your white shirt has grown
thirsty dark brown roses.
Your blood oozes and flees a
round the corners of your sash.

Ew. Ordinarily, roses are pretty. Here, though, they represent the nasty wound that the speaker has just pointed out. The speaker's friend describes the blood seeping through the speaker's nice, white shirt as dark, brown roses. That's a pretty metaphor describing a majorly gross sight. The blood has stained the shirt brown. What's more, it is still flowing around the corners of the speaker's sash. The friend notes that it "flees," which personifies the blood by giving it the human characteristic of running away in fear.

But now I am not I,
nor is my house now my house.

Man, this friend is just no help at all. Once again, in reaction to the speaker's discussion of his terrible wounds, the friend reminds the speaker of this own problems.
These lines are the second refrain in the poem, and remind the speaker—and us—that there are more fundamentally damaging wounds than bleeding from one's chest. In the friend's defense, we imagine it must be hard to do anything at all if you don't know your surroundings, or your self as yourself anymore.

--Let me climb up, at least,
up to the high balconies;
Let me climb up! Let me,
up to the green balconies.

Okay, says the speaker, how about option 3? If you can't help me trade for the green girl's stuff, and you can't help me die in my own bed, how about a little excursion?
It's interesting to note that the speaker is asking his friend here as if the friend were the one who had the power to stop him from climbing up to the high balconies. (To be fair, friends don't let friends with sucking chest wounds climb high balconies.) If the friend can't help him in any way, why would he be able to stop him from climbing? Or is the speaker even talking to his friend here? What do you think?
Regardless, this trip seems important to the speaker. The color of the balconies reminds us that the unreachable girl is up there, so the speaker's desire to attain her returns again with these lines.

Railings of the moon
through which the water rumbles.

Man, those are some pretty high balconies. Their "railings" belong to the moon, which would be a loooooooong climb.
Again, we have a confused visual image here. Once more, the balcony is associated with water. But, moonwater, now? Or is this water from the "bitter sea" that the girl on the balcony is dreaming in line 24? Either way, we're reminded that the balcony and water are linked.