The title points to Don Quixote, the dreamer knight of Cervantes, and the poem seems to catch him just after his adventures, back in his own house. The speaker is brief and a little puzzling here. The door is "great as a wish," which suggests that coming home still carries the size of a dream, as if the threshold were something he had long hoped for. But in the next breath it is "poor as the prince of a closet," a phrase that shrinks the grandeur into something cramped, shabby, and slightly comic. A prince of a closet rules almost nothing.
That gap between big wishes and small reality seems to be the heart of the poem. The "new black cloak" at the end adds a sombre note, perhaps hinting at mourning, disguise, or a plain end to the show. The mood is wistful and quietly deflated, with a touch of dry humour. Judging by the imagery, the speaker feels both tenderness and disappointment: home is longed for, yet it can't live up to the adventure.