“The greatness of human actions is measured by the inspiration that it brings. Blessed is he who carries within himself a God, an ideal of beauty and obeys it: an ideal of art, ideal of science, ideal of country, ideal virtues of the Gospel! These are the wellsprings of great thoughts and great actions. All reflections illuminate infinity.”

Variant translations:
Blessed is he who carries within himself a God, an ideal, and who obeys it: ideal of art, ideal of science, ideal of the gospel virtues, therein lie the springs of great thoughts and great actions; they all reflect light from the Infinite. (As quoted by Sir William Osler in his introduction to The Life of Pasteur (1907) by Rene Vallery-Radot, as translated by R .L. Devonshire (1923)
Blessed is he who carries within himself a god and an ideal and who obeys it — an ideal of art, of science, or gospel virtues. Therein lie the springs of great thoughts and great actions; they all reflect light from the Infinite. (As quoted in The Wordsworth Dictionary of Quotations (1998) by Connie Robertson, p. 320)
Discours de réception de Louis Pasteur (1882)
Original: (fr) La grandeur des actions humaines se mesure à l’inspiration qui les fait naître. Heureux celui qui porte en soi un Dieu, un idéal de la beauté et qui lui obéit : idéal de l’art, idéal de la science, idéal de la patrie, idéal des vertus de l’Évangile! Ce sont là les sources vives des grandes pensées et des grandes actions. Toutes s’éclairent des reflets de l’infini.