There is a famous and often quoted sentence by Albert Einstein, which reads:
Für uns gläubige Physiker hat die Scheidung zwischen Vergangenheit, Gegenwart und Zukunft nur die Bedeutung einer wenn auch hartnäckigen Illusion.
It was written in a condolence letter to the family of his deceased friend Michele Besso, and short before Einstein's own death.
I'm in doubt about the exact meaning of gläubig here. In general, if I understand correctly, this adjective may refer either to someone believing in a specific religion, or to someone who is trustful in something, not necessarily of a religious character. In different translations into English or Italian, I find uns gläubige Physiker translated in different ways, mostly “us believing physicists” and “us, who believe in physics”.
Is there any element – as far as possible internal to the text and to German language and as little as possible resorting to other Einstein's texts and what we generally know about him – that can actually lead us to understand that this occurrence of gläubig is to be considered as a secular concept rather than a religious one?
EDIT: Source for the quote: Pierre Speziali (Hrsg.): Albert Einstein – Michele Besso. Correspondance 1903–1955, Hermann, Paris 1972 (the standard edition of Einstein-Besso letters, with the German text and the French translation); the letter quoted here is dated 21 March 1955. The quote itself appears in several other books, for instance here and here. On Christie's website there is a reproduction of the manuscript letter.