From "Subtle is the Lord-- " : the science and the life of Albert Einstein by Abraham Pais, Oxford University Press, Oxford & New York, 1982.
'Science without religion is lame, religion without science is blind.' So Einstein once wrote to explain his personal creed:
"A religious person is devout in the sense that he has no doubt of the significance of those super-personal objects and goals
which neither require nor are capable of rational foundation."
His was not a life of prayer and worship. Yet he lived by a deep faith--a faith not capable of rational foundation--that there are laws of Nature to be discovered. His lifelong pursuit was to discover them. His realism and his optimism are illuminated by his remark:
'Subtle is the Lord, but malicious He is not' ('Raffiniert ist der Herrgott aber boshaft ist er nicht.'.').
When asked by a colleague what he meant by that, he replied:
'Nature hides her secret because of her essential loftiness, but not by means of ruse'
('Die Natur verbirgt ihr Geheimnis durch die Erhabenheit ihres Wesens, aber nicht durch List.').