By 'revelation' I mean that Jesus was an historical personage, who emerged from a lineage and a prophetic tradition of the 'Old Testament' who left record of his life teachings in The Gospels, and this is expanded and interpreted in the later parts of the New Testament...
But the incarnation, death and resurrection changed the structure of reality. The divine creator of earth became a man, died and was resurrected; and that changed reality. The universe before and after Jesus was a different universe.
That is the 'cosmic' Christ; and it does not depend on revelation. It happened: everywhere and to everybody and everything.
What happened? Well, should not look for a complete answer in a brief-statement form (when the universe is changed, a lot happens!) - but a part of it was that the cosmic Christ enabled Men to become fully divine eventually - and in this mortal life to experience - if we choose - the divine mode of consciousness.
The divine mode of consciousness is what I have termed Primary Thinking, what Rudolf Steiner sometimes calls the Imaginative Soul (coming after the Consciousness Soul), what Owen Barfield calls Final Participation and the highest level of consciousness described in William Arkle's A Geography of Consciousness.
This means thinking-from our real (which is divine) self; an activity that has direct knowledge of reality, and participates in God's work of creation (it is what Tolkien called 'subcreation).
That is (an aspect of) the Cosmic work of Christ.