The external image goes out from within.
Words are symbols. The fact that we can put them together in ways that are grammatically and syntactically correct does not assure us of describing reality, or even possibility. When we attempt to describe the post profound facets of our existence, words become more and more limited. We have to suspect every one.
Immortality exists as a concept because of mortality. 'God' would have to be more than immortal, as there could be no contrast, no opposite, wherein 'God' were not living. Life, death and immortality must be part of 'God', thus 'God' must be more.
So, when we say that 'God' must be inexpressible, we already say too much.