Mark 14:6 "Leave her alone. Why do you trouble her? She has done a beautiful thing to me."
“It is never too late to be what you might have been.” George Eliot
God isn't bluffing - He laid His cards down, now it's our turn.
Abraham understood that this was a job he had to tend to personally. Just like God understood that the redemption of mankind was a personal journey He had to take. No one else could do it for him, none of his paid servants could offer Isaac for him – this was his sacrifice, his journey. He stopped life to make it happen.