Christian existentialism evolved because of Jean Paul Sartre's definitive proof that God could not exist as we exist. Jesus existed as we exist therefore cannot be God based solely on this proof let alone any other facts.

As contrasted with Existence, Being is all-embracing and objective rather than individual and subjective. Being includes both Being-in-itself and Being-for-itself, but the latter is a nihilation of the former. Christin proofs of God's existence pose God as a pour-soi [a being-for-itself; a consciousness] who is also an en-soi [a being-in-itself; a thing]: which is a contradiction in terms.

"Being-for-itself" is the nihilation of Being-in-itself; consciousness conceived as a lack of Being, a desire for Being, a relation to Being. By bringing Nothingness into the world the For-itself can stand out from Being and judge other beings by knowing what it is not. Each For-itself is the nihilation of a particular being. It is the human way of Being which is fluid and open to possibilities and imagination.

"Being-in-itself" is non-conscious Being. It is the Being of the phenomenon and overflows the knowledge which we have of it. It is a plenitude, a fixed and complete being, and strictly speaking we can say of it only that it is. It has no relation to itself or to anything else.

Quoting from Sartre in Simone de Beauvoir's 'Adieux: A Farewell to Sartre' (Translated by Patrick O'Brian; Penguin; London:1984) p 436 - 443 ... interviews with Sartre just before his death

[DB = De Beauvoir S = Sartre]

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DB: And when you wrote Being and Nothingness did you vindicate or try to vindicate your disbelief in God philosophically?

S: Yes, of course, it had to be vindicated. itried to show that God would have to be the "in-itself for itself," that is, an infinite in-itself inhabited by an infinite for-itself, and that this not of "in-itself for-itself" was it self contradictory and could not consitute a proof of God's existence. ...

***************************************************** Sartre also said "existence preceeds essence" and thus destroyed the majority of Christian thinking up to his time (though many are stuck in the 19th century still talking about the essences of the particular bits of the trinity). To quote Sartre explaining this ... "man first of all exists, encounters himself, surges up in the world - and defines himself afterwards." Since existence precedes essence, it follows from the meaning of the term sentient that a sentient being (such as God) cannot be complete or perfect.

God does not EXIST ... God is that from which existence proceeds. God is supra-existence. To say that God exists is to devalue and reduce God. Existence is a quality of things that are created by God. God is that from which existence is created and sustained and therefore God cannot be that which he makes and sustains.