“They tell us of the fixed laws of nature! but who dares maintain that He who fixed these laws cannot use them for the purpose of answering His people's prayers?”

Speech to the Conference of the National Union of Conservative and Constitutional Associations in Oxford (23 November 1887), quoted in The Times (24 November 1887), p. 7
1880s

Source: Anarchism and Other Essays

2015, Remarks to the Kenyan People (July 2015)
Context: Because corruption holds back every aspect of economic and civil life. It’s an anchor that weighs you down and prevents you from achieving what you could. If you need to pay a bribe and hire somebody’s brother -- who’s not very good and doesn’t come to work -- in order to start a business, well, that’s going to create less jobs for everybody. If electricity is going to one neighborhood because they’re well-connected, and not another neighborhood, that’s going to limit development of the country as a whole. If someone in public office is taking a cut that they don't deserve, that’s taking away from those who are paying their fair share. So this is not just about changing one law -- although it's important to have laws on the books that are actually being enforced. It’s important that not only low-level corruption is punished, but folks at the top, if they are taking from the people, that has to be addressed as well. But it's not something that is just fixed by laws, or that any one person can fix. It requires a commitment by the entire nation -- leaders and citizens -- to change habits and to change culture. [... ] People who break the law and violate the public trust need to be prosecuted. NGOs have to be allowed to operate who shine a spotlight on what needs to change. And ordinary people have to stand up and say, enough is enough.

Book I, line 479.
Astronomica

The Notebooks of Leonardo da Vinci (1883), X Studies and Sketches for Pictures and Decorations

1960s, Memorial Day speech (1963)
Context: The law cannot save those who deny it but neither can the law serve any who do not use it. The history of injustice and inequality is a history of disuse of the law. Law has not failed — and is not failing. We as a nation have failed ourselves by not trusting the law and by not using the law to gain sooner the ends of justice which law alone serves. If the white over-estimates what he has done for the Negro without the law, the Negro may under-estimate what he is doing and can do for himself with the law.

Source: Lullaby (2002), Chapter 39

Remarks at "Loyola College Alumni Banquet, Baltimore, Maryland (18 February 1958) http://www.jfklibrary.org/Research/Research-Aids/Ready-Reference/JFK-Quotations.aspx; Box 899, Senate Speech Files, John F. Kennedy Papers, Pre-Presidential Papers, John F. Kennedy Presidential Library
Pre-1960