The splendor of the goal of the French Revolution is simultaneously the source of our strength and of our weakness: our strength, because it gives us an ascendancy of truth over falsehood, and of public rights over private interests; our weakness, because it rallies against us all vicious men, all those who in their hearts seek to despoil the people . … It is necessary to stifle the domestic and foreign enemies of the Republic or perish with them. Now in these circumstances, the first maxim of our politics ought to be to lead the people by means of reason and the enemies of the people by terror. If the basis of popular government in time of peace is virtue, the basis of popular government in time of revolution is both virtue and terror: virtue without which terror is murderous, terror without which virtue is powerless. Terror is nothing else than swift, severe, indomitable justice; it flows, then, from virtue.

Maximilien Robespierre (1758-174) French lawyer, politician, revolutionary leader

Speech, National Convention (7 May 1794)
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In a parallel thought, he wrote in On the Principles of Political Morality (1794):

If virtue be the spring of a popular government in times of peace, the spring of that government during a revolution is virtue combined with terror: virtue, without which terror is destructive; terror, without which virtue is impotent. Terror is only justice prompt, severe and inflexible; it is then an emanation of virtue; it is less a distinct principle than a natural consequence of the general principle of democracy, applied to the most pressing wants of the country.