My dear Theo, Feeling, even a fine feeling, for the beauties of nature isn't the same as religious feeling, although I believe that the two are closely connected. The same is true of a feeling for art. Don't give in to that too much either. Hold fast especially to your love for the firm [of the Paris' art dealers Goupil, where both brothers worked - Vincent started in 1869 and Theo in 1873] and for your work.... Nearly everyone has a feeling for nature, some more than others, but there are few who feel that God is a spirit, and that they must worship Him in spirit and in truth. Pa is one of the few, Ma too, and also Uncle Vincent, I believe.

quote from his Letter #049 to Theo on 'religious feeling' (Paris, 17 Sept. 1875)