Section 13 Summary

Lines 99-101

Sing on, sing on you gray-brown bird,
Sing from the swamps, the recesses, pour your chant from the bushes,
Limitless out of the dusk, out of the cedars and pines.

• Aaaand, there's that bird in the swamp again. We know how important singing is to the speaker at this point since expressing oneself (writing this poem, or "singing") is the only thing one can really do when in mourning. 
• We're seeing the symbolism of the bird a little more clearly now that seems to indicate expression, and more specifically the speaker's expression. We can't blame it, really. We all have that little bird inside of us that needs to be expressed, especially when grieving.
• The "recesses" in line 100 also indicate the solitary nature of the speaker's voice, symbolized by the singing bird. All the same, the song is "limitless" as it pours out from the "bushes" at "dusk" (sunset). Again, we get the idea that life and expression persist in the face of darkness, or loss of light (like at dusk).

Lines 102-103

Sing on dearest brother, warble your reedy song,
Loud human song, with voice of uttermost woe.

• We get another nod of connection to this singing little bird, as the speaker calls him "dearest brother." (Probably they're not related.) 
• Line 103 specifies that song as a "loud human song," which clarifies the bird's act of singing in a more humanizing way. The "loud" part tells us that this song isn't the sort of thing that can be silenced. 
• The second half of 103 explains why that loud song cannot be silenced: it comes from a "voice of uttermost woe." With that level of woe, the song must be sung and the singer must express that inner bird inside of him. All the woe needs to go somewhere and can't be bottled up inside.

Lines 104-107

O liquid and free and tender!
O wild and loose to my soul—O wondrous singer!
You only I hear—yet the star holds me, (but will soon depart,)
Yet the lilac with mastering odor holds me.

• Line 104 gives us a kind of metaphor for the human song that's "liquid and free and tender." And line 105 connects the song directly to the soul in a kind of "wild and loose" celebration. The singer, despite his woe, is celebrating—and celebrated—here for the wonder he creates through his song. So even if it's woeful, it's still beautiful and "wondrous" in its own way.
• The bird's song is also rather captivating, since the speaker says in line 106 that he only hears the singer, even though we're reminded that the "star holds [him]" (i.e., he still mourns its loss). Immediately after though, the speaker concludes that the star will "soon depart." 
• So although the speaker can't quite let go of the one he loves, he's seeing and hearing things in a more uplifting sort of way because of the hermit-bird's song. 
• The song is therefore one that reflects life's wonder, beauty, and freedom. It may be woeful, but it's also a reminder of life's wonder and the limitless human spirit that can transcend woe through song and soulful expression. 
• Then again, line 107 is another honest reminder of those lilacs that have a "mastering odor." So the speaker looks as if he's still flip-flopping between the more uplifting stuff and the woe he still feels and is reminded of when he smells those lilacs. Sniff, sniff.