Voltaire, Toleration and Other Essays 
Voltaire: Treatise on Tolerance - Constitution Society
This collection of essays by Voltaire contains a long essay on the Jean Calas case, several shorter essays on religious topics, and his famous poem on the Lisbon earthquake.
Toleration and Other Essays - Online Library of Liberty
The selection opens with the which has a mainly historical interest, and illustrates the finest side of Voltaire’s work and character. It shows him as a profound humanitarian, putting aside, in his seventieth year, his laughter and his comfort to take up the cause of an obscure sufferer, and shaking France, as Zola did in our time, with his denunciation of a judicial crime. The story of the crime is told in the essay itself; but it is not told, or in any way conveyed, that, but for the action of the aged rationalist, not a single effort would have been made to secure redress. His splendid action on that and a few similar occasions has been held by critical students of his career to atone for all his errors. Many Protestants who scoff at “Voltaire the scoffer” may learn with surprise that his noble and impassioned struggle earned for them the right to live in Southern France. The treatise was published in 1763. I have omitted a number of lengthy and learned notes and one or two chapters which are incidental to the argument and of little interest to-day.