The poem imagines that dark ages don't arrive with a bang. They come with soft, ordinary names: Ease, Lack, and Tomorrow. Comfort, scarcity, and putting things off are the forces that dim a society, and the speaker says they slip into "any ear / as kindly as blood," as if they were natural, even nourishing. Nobody feels attacked. That is exactly the danger.
The title, "Prophet," suggests the speaker sees this coming, but the last lines turn the poem sour. "I am not to blame / if I turn a profit" sounds like a shrug, a defensive excuse. The prophet may be cashing in on the very darkness he describes, or simply benefiting from a world that is too comfortable to listen. The poem leaves that uncertain.
The mood is cool, wry, and a little uneasy. The speaker's calm tone makes the warning feel more chilling, and the closing disclaimer leaves a faint sense of guilt hanging in the air.