Re: Secret behind Obito's Kamui?
I think you're confused in your analogy. Most priests will explain that the "word" of God is the bible, or the inspiration for the bible (depending on the level of insanity). Jesus was claimed to be God's son, not his "word".
What Amuro said is correct. Banbutsu Souzou is what created the Bijuu, not Izanagi. Izanagi is considered the "practical application" of Banbutsu Souzou because it turns one's imagination into reality (the Sage imagined the Juubi's chakra weakened and separated it into 9 parts, and imagined containers for the divided chakra to create the Bijuu). The difference is that while Banbutsu Souzou can create living creatures like the Bijuu, Izanagi cannot. It has never even been implied to have that capability, in any event that it has been used. It only blurs the line between reality and imagination for the caster and allows them to avoid death by turning their death into an illusion, or a figment of their own imagination. That is where Izanagi was derived from Banbutsu Souzou, using Yin to create a figment of the user's imagination (not dying) and Yang to "breathe life" into that figment (turning one's death into an illusion).