Joy & Woe are woven fine, A Clothing for the Soul divine; Under every grief & pine Runs a joy with silken twine.
Blake continues on the "Joy and Woe" theme. These four lines are rubbing elbows with the four lines that came before them for a reason.
But what Blake's saying in this case might be a little harder to understand. Why are joy and woe "woven fine"? And why are they the hot, new Urban Outfitters garb that the Soul is wearing?
Well, since humans (and all living things, according to Blake) have souls, their experiences in the world become like a kind of clothing. Like people say, "It builds character"—joy and woe wrap the soul in experience, giving it a unique character and identity. They make it an individual.
So, the idea that joy and woe are like threads weaving together a garment is a strange and unexpected metaphor. It's the kind of interesting, left-field thing Blake specializes in.
The last two lines help prop up a point made in the last section: joy and grief are complementary. You can't have one without the other. A joy is somehow hidden under every grief, waiting to balance it out and harmonize it. The fact that joy is made of "silken twine" indicates the high quality, Versace-level elegance and subtlety of joy as an emotion.
Note how Blake uses the similar sounds of "woe" and "woven" for an effect. Check out "Sound Check" for all the goods.