“Every beginning is difficult, holds in all sciences.”

The Story of Philosophy (1926)

Source: A Year to Live: How to Live This Year as If It Were Your Last

Quoted in The Black Book of Clark Ashton Smith (1979)

Scientific Autobiography and Other Papers as translated by F. Gaynor (1949), p. 184
Variant translations:
Both religion and science need for their activities the belief in God, and moreover God stands for the former in the beginning, and for the latter at the end of the whole thinking. For the former, God represents the basis, for the latter – the crown of any reasoning concerning the world-view.
Religion und Naturwissenschaft (1958 edition), p. 27, as quoted in 50 Nobel Laureates and Other Great Scientists Who Believe in God (2008) by Tihomir Dimitrov http://nobelist.tripod.com/sitebuildercontent/sitebuilderfiles/50-nobelists.pdf
While both religion and natural science require a belief in God for their activities, to the former He is the starting point, to the latter the goal of every thought process. To the former He is the foundation, to the latter the crown of the edifice of every generalized world view.
Scientific Autobiography and Other Papers (1968 edition)
Religion and Natural Science (1937)

Message to the Tricontinental (1967)
Context: The beginnings will not be easy; they shall be extremely difficult. All the oligarchies' powers of repression, all their capacity for brutality and demagoguery will be placed at the service of their cause. Our mission, in the first hour, shall be to survive; later, we shall follow the perennial example of the guerilla, carrying out armed propaganda … the great lesson of the invincibility of the guerrillas taking root in the dispossessed masses; the galvanizing of the national spirit, the preparation for harder tasks, for resisting even more violent repressions. Hatred as an element of the struggle; a relentless hatred of the enemy, impelling us over and beyond the natural limitations that man is heir to and transforming him into an effective, violent, selective and cold killing machine. Our soldiers must be thus; a people without hatred cannot vanquish a brutal enemy.

As quoted in "A close encounter with Chris Carter" at Salon (28 April 2000) http://www.salon.com/2000/04/28/chriscarter/
Context: The most difficult thing to reconcile is science and religion … And so we created a 
dilemma for her character that plays right into Mulder’s hands. So that cross she wears,
 which was there from the pilot episode, is all-important for a character who is torn 
between her rational character and her spiritual side. That is, I think, a very smart
 thing to do. The show is basically a religious show. It’s about the search for God. You 
know, "The truth is out there." That’s what it’s about.

Real Time (2002)