A man who should act, for one day, on the supposition that all the people about him were influenced by the religion which they professed would find himself ruined by night.

Macaulay’s remark is a sharply skeptical observation about the gap between public profession and private conduct. It suggests that taking people’s stated religious commitments as a reliable guide to their behavior—especially in practical affairs like money, power, or self-interest—would be disastrously naïve. The line functions less as an attack on religion itself than as a comment on human inconsistency and hypocrisy: moral ideals may be sincerely affirmed, yet frequently fail to govern everyday actions. In Macaulay’s Whig, worldly outlook, the quote also implies that social and political life must be understood through incentives, institutions, and character rather than through pious declarations alone.