A living faith is animated by doubt. Faith dies when it hardens into a subjective certainty and a moribund complacency. I have had this thought for years. Each time I re-enact it, it strikes me as true. I was pleased to discover recently that T. S. Eliot holds the same or a very similar view:
'For people of intellect I think that doubt is inevitable,' Eliot once told an interviewer. The doubter is a man who takes the problem of his faith seriously.'
The quotation is from the outstanding 712 pp. biography by Lyndall Gordon, T. S. Eliot: An Imperfect Life, W. W. Norton & Co, 1998, p. 112.
Doubt, the engine of inquiry, is the purifier of the quest for contact with that which lies beyond inquiry.