It's also a recurring theme in various religious texts and mythos...the idea of "God" becoming "man" or an "immortal" becoming "mortal". Very prevalent in the Greek, Celtic and Roman mythos. And was examined to a degree in various vampire series: Angel, Forever Knight, Moonlight, Being Human, and the Vampire Diaries. I think...it's a sort of reverse theme...humanity's fear of death and their own mortality....

God becomes man, suffers the physical torments of man, dies....and is reborn with a new understanding of what it is to suffer.