Our speaker's down in the dumps, but that doesn't mean that he can't dish up some heaping spoonfuls of symbolism and imagery in this poem. Take the wind, for example. It's a weighty symbol that's meant to emphasize his frame of mind. Rather than a gentle breeze, though, it's a fierce, howling gale that's more appropriate to his stormy mood.
Lines 4-8: The "Aeolian lute" in these lines acts as a metaphor for the sound that the wind makes. And you know what? It's not kicking up enough of a ruckus to match our speaker's mood. If it's just going to blow a little bit, he'd rather it not blow at all ("better far were mute") (8).
Line 15: The wind is not just a mirror of the speaker's mood. He wants it to blow in order to wake up his numb and depressed spirit.
Lines 97-107: After his general discussion of the importance of joy in the life of the soul, our speaker returns to the wind in these lines. Is it actually howling now? Remember that he complains earlier in the poem that it's not blowing hard enough. Perhaps, then, he's imagining the terrifying wind, which is more suitable for isolated mountain peaks, spooky witch's cabins, and devils' holiday parties. In other words, the dude is in a bad frame of mind.
Line 129: As much as he invites the wind to blow and rage, symbolizing his disturbed mindset, he hopes that his friend "Lady" only experiences brief versions of such a tempest, the kind that blow over quickly—like the storms over a mountain ("mountain-birth").