In just four lines, the speaker describes two odd acts of wanting. First, they build something precious: a "jade city" made so the heart can "have a heart in" it. That phrase loops back on itself, as if the heart needs its own inner room, a safe core inside the core. Jade suggests something beautiful, hard, and carefully worked, but a city of it also sounds cold and a little unreal. The title, "Contractor in hell," hints that this building happens in a grim place, with the speaker as a hired builder doing the job.
Then comes the surprise. The speaker hopes to be "possessed by evil," yet "very civilly." The humor is dry and unsettling, because evil is welcomed with good manners, like a guest being shown in. The speaker seems to want to feel something intense while keeping control and politeness intact. The mood is calm on the surface but uneasy underneath, mixing longing, irony, and a faint sense of self-protection.