Joy & Woe are woven fine, A Clothing for the Soul divine; Under every grief & pine Runs a joy with silken twine. (59-62)
So, we've said that Blake wasn't exactly a fashionista. But he's talking about clothes again, here—so maybe we were wrong. But these are symbolic, metaphorical clothes—making Blake a Ralph Lauren of the Mind (if you will). Joy and woe are experiences that the soul "wears"—it hasn't experienced them in the womb, but when it comes into the world, it gets a taste of happiness and suffering (and then some).
But joy is a fine, subtle emotion—which is why it's made of a rich fabric like silk. Woe is thick, coarse outerwear. In context, these lines are related to the discussion of woe and joy that comes in the lines immediately before them (55-58), expanding on the topic.