The speaker looks back on a single reckless day — “one riotous day” — and realizes how long and painfully he has had to pay for it. The debt is not money but regret, grief, and sorrow without relief. He accepts that the payment will continue for the rest of his life; only death, described almost gently as “the clasp of peace,” will release him.
The mood turns bitter in the last stanza, where he admits the original choice seemed small at the time. What he bought was slight, the loan poor, and yet the interest has become unbearable. The sudden cry “God! but the interest!” captures the shock of someone trapped by consequences far heavier than the act seemed to deserve. The poem creates a weary, remorseful feeling, edged with anger at how cheaply a lifetime of suffering was purchased.