So, it's actually a mistranslation (by Kubo probably). It's not YHWACH but actually JHWH/JAHWE :O (in some religions and believes, this is a true name of God). No wonder he tries to dethrone the Soul King, which a name like that, that's the only thing he would be aiming for in his life... this also explains the angel motive of his servants/soldiers and how he managed to survive for such a long time.
So the big plan is to absorb every fighter there currently is and obtain unimaginable amounts of power. So far Ishida Uryu is the only that can oppose him... looks like we can already guess what Uryu's Holy Complete Mode will be called, kukukuku...