At first I thought I heard a preponderance of dactyls in the poem's falling rhythms, but after a second reading, I don't think that's the case anymore. The poem is musical, yes, but it doesn't utilize meter--even in pieces--toward that end as much as it does smaller units of sound, namely its vowels and a few select consonants. The line that best exhibits what I'm talking about can be found 6 lines up from the bottom:
endlessness, nothing celebrates it except its mirror
Here I hear a whole lot of "S" and a bit of "R," the most-loved consonants in the poem, and I think I know why: they have great sustain. That is to say, they require time to be pronounced, "S" because it lingers on the tongue as a sibilant, and "R" because it is voiced first (as opposed to voiceless), and breathy second. As soft consonants, each requires breath as it expires, as in endlessness and mirror. You can't stop those words--those sounds--short. Even after the vocal cords have have quit, they continue as a whisper (hmmm...whiSpeR...).
In the poem, "S" and "R" can be found everywhere, thus slowing the poem's pace and effectively granting it a serenity (hmmm...there they are again. coincidence?) apropos of the poem's content--it's something of a tranquil, romantic piece about poetry, possibly a lover. In the above quoted line, that slow, steadiness is easy to hear. In that case, too, the lack of monosyllabic words helps steady the pace and tone: "endlessness, nothing celebrates it except its mirror". And, the line is long. Although line length in and of itself is not necessarily the cause of rhythmic poetry, a longish line does have a tendency to allow rhythms to build in a way that a shorter line--simply due to its length--cannot. Consider this hacking of the Darwish line:
except its mirror
Its continuity is broken now, not only into three lines, but into relative arrhythmia. The consonants, especially the "S," no longer have their sense of contiguity, thus the music falters.
As for the vowels, Darwish-through-Joudah likes them long, especially his "I." This is for the same reason he likes his "S" and "R": a long vowel is drawn out over time, and a short vowel is clipped. Thus, an abundance of long "I" and "E" and so on is likely to slow the poem's pace and help its tone settle into a calm.
If you're not buying this business about the sounds of vowels and consonants, consider a few words we use for bodies of water. I'll list them in the order from small, insignificant bodies to large, demanding ones. Note the use of hard and soft consonants as well as the use of long and short vowels. Picture in your mind the image as you listen to the sound of each word: crick, creek, pond, river, lake, sea, ocean. Maybe I'm being far-fetched, but the sound of each water word seems indicative of the size and presence of the body it represents. A crick is something that runs through the woods near your backyard. Maybe it contains some small fish. It certainly begins and ends with a hard consonant and shoves a short, stubby vowel in the middle. A sea is vast, virtually endless to the eye, though the brain is wiser (and deeper...). Like the word that represents it, it just sort of disappears silently off the horizon. It hits the shore with an "S" and ebbs back to the edge of the Earth with an "E."
Anyway, the first line of "Your Night is of Lilac" demonstrates what I'm talking about with regard to the poem's sounds:
The night sits wherever you are. Your night
"S" and "R" are there of course. Then we have the long "I" repeated in the word "night," the long "O" in "Your." Particularly, it's that pair of long vowels and the consonance of "R" at the end of the line that really extends the line's music. The beginning of the next line, too, is constructed in sharp contrast to this extension, highlighting those opening sounds in effect: ". . . is of lilac" is read quickly, running over its lone long "I" with the preceding short one and the hard "C" with which it ends. Interestingly, the poem slows and becomes rhythmic again for another line and a half or so, only to be clipped at "and lights up" in line 4, a nice echo of "lilac" in line two in terms of sound and placement.
I could go on, but I don't care to parse "Your Night is Lilac" any further. And that's pretty much the hard and soft, the long and short of it. As for content, I think that line about endlessness pretty well says enough. I also like "Night / is the covenant of night." This is a love poem after all, and well, what else is there to say?