People in those old times had convictions; we moderns only have opinions. And it needs more than a mere opinion to erect a Gothic cathedral.

Heine contrasts the moral and religious certainty he associates with the medieval past (“convictions”) with what he sees as modernity’s more tentative, debatable stance (“opinions”). The Gothic cathedral functions as a symbol of collective, long-term cultural achievement: such buildings required generations of coordinated labor, shared faith, and a unifying worldview that could justify immense sacrifice. By implying that “mere opinion” cannot produce such works, Heine critiques modern skepticism and fragmentation—suggesting that without deep commitments, societies may lose the capacity for grand, enduring creations. The remark is less nostalgia than a pointed diagnosis of modern spiritual and cultural disunity.