No history book would record the name of John Baptiste. No monuments would be built to his memory, no holidays or worlds or cities would be given his name. Yet it was his action that would trigger the greatest change mankind had experienced in ten thousand years. The moment took place upon a world whose name does not matter, one of thousands of worlds that are at any given moment under siege by the enemies of Man. John Babtiste was one of thousands of Imperial Guards who had been thrown into the path of a great tide of Orks, thrown away as a barricade, to buy time for the arrival of the Space Marines and time for the second, larger, division of the Guard to fortify itself against the Orkish tide.
His division had been shattered, crushed before the oncoming tide, and John lay dying, his blood gushing out from a massive choppa wound. With his dying words, he whispered, "Emperor, into your hands I commit my spirit."
In the Warp, that prayer and that faith took on shape and power. It was a tiny speck, a mere grain of sand in comparison to the planetary bodies of power that the Gods threw around, but it existed. Through the Warp it sped with the speed of thought, weaving around daemons and slipping through palaces. Finally, it came to a place, deep within the Warp, far above or below or beside reality. A vast edifice of power hung there, like an intricate diagram in many dimensions, forged of prayers and woven of faith. Yet one tiny flaw marred the beauty of the whole, one infinitesimal gap still remained to complete the intricate and awesome symmetry of the whole. The tiny spark of John Baptiste's final prayer flitted into that gap, became a tiny length of power that slotted perfectly into the equally tiny gap in that vast matrix of power, and that one tiny spark completed the entire whole, provided the last spark necessary to complete the massive edifice.
Its structure complete, the matrix collapsed in on itself, like the cloud of gas condensing into a newborn star. From end to end the Warp rang with the power of that collapse, of that awesome fusion of vast energies. And in that crucible of refined faith and tangible belief, a new entity took shape. On the Golden Throne of Terra, the Emperor's shattered body disintegrated in a flash of pure power, a flash that burnt his mortal shell to subatomic particles. And in the Warp, the newborn God opened eyes as vast as the universe, flexed limbs of pure will. Ornate armor inscribed with sigils of white fire, a sword of light in his hand, eyes that shone like suns, skin like burnished gold. The Emperor Undying, God and Defender of Mankind.
A wave of golden light exploded outwards from Terra, slashing along the boundary between the Warp and the Materium at many thousand times the speed of light. Wherever the light passed, the powers of Chaos were banished from the Materium. In a single vast flash, the Eye of Terror slammed shut. Daemons exploded in golden fire, their essence forcibly returned to the Warp. Cultists were cleansed, the accumulated gifts and curses of the Ruinous Powers stripped from them, sometimes lethally.