What then is the physical carrier of that Spiritual which works in the ethereal? (For we may say, the ethereal represents the lowest kind of spiritual working). What is the physical carrier which is so permeated by the ethereal that the ethereal, moistened once more with sulphur, brings into it what it has to carry — not in Formation this time, not in the building of the framework — but in eternal quickness and mobility into the midst of the framework? This physical element which with the help of sulphur carries the influences of life out of the universal ether into the physical, is none other than oxygen. I have sketched it here in green. if you regard it physically, it represents the oxygen. It is the weaving, vibrant and pulsating essence that moves along the paths of the oxygen. For the ethereal moves with the help of sulphur along the paths of oxygen. (Steiner 2007:23)
It is difficult to come to an understanding on these matters which the physicists and chemists, for — by the methods they apply — from the very outset the oxygen must always be drawn out of the earth realm; hence they can only have dead oxygen before them. There is no other possibility for them. That is the fate of every science that only considers the physical. It can only understand the corpse. In reality, oxygen is the bearer of the living ether, and the living ether holds sway in it by using sulphur as its way of access. (Steiner 2007:23)
STEINER, Rudolf. 2007. The Agriculture Course. (Trans.: George Adams) Shrewsbury: Wilding & Son Ltd.