We must, however, be clear that all that makes itself visible to our eyes derives from the spirit. There is no material thing that does not have a spiritual basis.
Now for a more frequently-used analogy. A child shows us some ice. We say, “This is water in another form.” The child will then say, “You say that it is water but yet it is ice.” Whereupon we will say, “You do not know how water becomes ice.” So it is for him who does not know that matter is condensed spirit.
Source: Rudolf Steiner – GA 56 – Illusory Illness – Munich, December 3, 1907