In Steiner's terminology, there are two aspects to what is often described as a single being in conventional Christian theology. This is the figures of Lucifer and Ahriman. Ahriman is the tendency embodied by the traditional hoofed devil that might come to our minds. Lucifer, by contrast, is that angel of light who fell for refusing to obey God. In the Muslim account, the angel Iblis refused God's order to bow before Adam. Iblis gives the reason that he should only bow to God, not to a less being, nonetheless he is cast out of heaven for his disobedience. The Sufi poet Rumi considers Iblis to be a paradoxical role model for us as human beings: we should bow before no one but God.
If we consider the serpent image, it is the belt of time introduced by the Fall. It is the cycle of karma, the seemingly endless wheel of dying and suffering. As Valentin Tomberg writes in his posthumously (and anonymously) published Meditations on the Tarot: Journeys in Christian Hermeticism, the serpent represents the unredeemed inheritance from the past: the prejudices of our upbringing and even our lower animal impulses. These must be transmuted. If we merely indulge the shadowy instincts of the hardened past, that is Ahriman. If, on the other hand, we indulge the wishful thinking of the future, that is Lucifer. One might almost say that Ahriman is the shadow of Lucifer.
In Aristotle's philosophy, courage as a virtue is always a mean and an extreme. Courage is between the extremes of cowardice (Ahriman) and rashness (Lucifer). If you imagine an equilateral triangle, the two points at the base on the two harmful extremes of cowardice and rashness and the third point at the summit is courage. That is close to what Steiner means when he speaks of the Christ impulse as being "between" these one-sided extremes.
For those familiar with Tolkien's Lord of the Rings villains, Sauron dissolves everything into a dreadful triumphant conformity whereas Saruman splits light into its constituent parts and creates a genetically engineered race of orcs. Saruman is Ahriman with an S added in the front. Sauron is Lucifer. And the Christic impulse is championed by the fellowship, especially in the sacrificial nature of Gandalf the white.
The balancing element in this world, that overcomes both, is the Christ impulse which is always about bringing harmony to disharmony, to heal the sick. In our bodies, if our arteries are too Ahrimanic, that is arteriosclerosis. If our circulatory system is too soft, it tends towards necrosis, which is Luciferic. When Jesus Christ says "I am the way, the truth, and the life" this, for Steiner, is not merely a metaphor. In Biodynamic farming, it is about restoring life to the soil, vitality to dead earth, and truth where there is falsehood. Steiner repeatedly reminds his listeners, "Don't believe what I say, think through it for yourself."
As Goethe says, "Only that which is fruitful is true."