Zen Koan: Bodhidharma's Vast Emptiness

The Emperor asked of Bodhidharma,
“What is the ultimate meaning of the holy truth of Buddhism?”
Bodhidharma replied, “Vast emptiness. No holiness.”
The Emperor asked, “Who stands here before me?”
Bodhidharma replied, “I don’t know.”

Note: Who is the one reading? What is the ultimate meaning? Of Christianity? Humanity? Steem?