I have always regarded that Constitution as the most remarkable work known to me in modern times to have been produced by the human intellect, at a single stroke (so to speak), in its application to political affairs.

Gladstone is praising a particular written constitution—almost certainly the U.S. Constitution—as an extraordinary feat of political design. The emphasis on “at a single stroke (so to speak)” highlights his amazement that a durable framework for government could be drafted in a relatively concentrated moment rather than evolving slowly through custom and precedent. The remark also reflects a 19th‑century British statesman’s perspective: Britain’s constitution was largely unwritten and accretive, so the American document could appear uniquely “intellectual” and deliberate. The quote elevates constitution-making as a rare instance where abstract reasoning, compromise, and practical governance converge into a coherent, lasting instrument.