So, we admit: this guy (and we're just assuming it's a "he") is a bit down on his luck. We're guessing, anyway, that being stuck in a seventeenth-century prison is really not that much fun. No fitted sheets. No complimentary WiFi. And definitely no mint on the pillow. All in all, our prisoner-speaker could be forgiven if he spent the whole poem bemoaning his fate.
But, this is no ordinary speaker, folks. He's defiant. He's an optimist. More than anything, though, he's got imagination. Sure, things might look bad if you just used your eyes, but he's able to use his mind to soar beyond the confines of his cell. He imagines his loved one, his friends, and his art. In short: he's got everything he could ask for, stored right up there in his noggin'.
Know what else? Thanks to the comforts of his mind, this speaker is going to shout his support of the king—the thing that got him tossed in jail in the first place—from the highest rooftops. He's confident in himself, in his art, and, most importantly, in the power of his imagination to overcome something as minor as a prison cell. What a guy!