The poem opens on a calm, bright image: a morning with fine, clear frost. But the mood turns quickly. Winter, the speaker says, makes us fear, drink, bet, and "sin better," and it leaves us with "time lost." The cold morning is beautiful, yet the poem treats the season as a kind of bad influence, pushing people toward fear and small vices.
The title is a twist on the familiar saying "a mind is a terrible thing to waste." Here it becomes "a mind of winter," which suggests a mind dulled or darkened by the season, and the poem seems to show that mind wasting itself on drink, gambling, and idleness. The line breaks are short and clipped, which gives the poem a cold, bare feel, and the final phrase, "time lost," lands with a thud.
The speaker sounds wry rather than angry, a little tired and a little amused at how predictable people are. Judging by the tone, the poem sets crisp beauty against a quiet sense of regret.