Francis Schaeffer claims that Sartre asserted (words to the effect) that without an infinite reference point man has no true meaning.
Now, I've not found that specific remark, or anything that directly echoes it in what I've read of Sartre...and life is too short to wade through Being and Nothingness without a PhD at the end, but I have read allusions to that in Existentialism is a Humanism and Nausea.
The idea is also consistent with what I recall of what Jaspers had to say in Philosophy of Existence. One only finds definition in some ultimate act of definition...and that is undefined. And, I would say undefinable when the self-experience is the locus of definition. It is a definition based on nothing which has a grounded basis. It floats arbitrarily unattached and truly undefined. So it has no 'meaning' (whatever that word now means) to even the one seeking definitive meaning.
So, lets clarify the conundrum to "without an infinite reference point there is no real self-knowledge."
We can only know ourselves in relation to others, in interpersonal relationships. There are no possible relationships in the non-personal world and any fake or imagined relations ships are in fact mute.
But if true significance ("meaning") comes only through relationships then there must always be a 'reference' relationship, let's say its one's parents. But this is not final. This reference relationship also needs a 'reference' relationship.
In a cosmos that is finally material, the final 'significance' has to be founded or grounded in some mute material thing or process. But it is inter-personally and therefore finally meaningless. It does not communicate, it reflects or responds to nothing of who one is and the only quality of the "relationship" is blank indifference. A nullity.
Yet we still have an inner quest for significance and live and relate as though this is a real thing.
An infinite regress explains nothing as it never ends in a final ground. It vanishes into the indefinably remote and unconnected other which results in the same abject indifference that the material cosmos characterizes.
True self-knowledge, significance or referentially secure "meaning" must remain the product of relationship. To be true and truly significant there must be a viable relational ground in which it terminates and gives a resolution or definition. A self-existent ground, an independent ontology.
Thus we need the Creator God who is person who sustains and anchors all relationship through being the ground and source of personhood and the final 'relater'.
Now the flip-side for the one who denies a Creator-God, who demands we applaud their faux independence and nonchalant self-applauding bravery.
The atheist's dilemma.
We all seek meaning, and often has it in life yet there can be no real axiological pay-off in a material cosmos, Whence the drive for, often achievement of 'meaning' or true significance? Each relies on an implicit teleology which is denied by the meaningless (literally) atheistic conception of termination.
Yet atheists typically act as though their teleological impulse is real while denying a real basis for the 'meaning' quest. So, what is it? The existentialist's self-defining grand act? But to what point? It all ends in dust and in the end no-one cares!
There is really no point, so an atheists has to explain to him/her-self why they even go to the doctor when feeling ill. That too is finally dust and a pointless way-post on the way to a pointless end.
Some provisional thoughts.