According to Merriam-webster...
"1 capitalized : the supreme or ultimate reality"
To say that God doesn't exist is like saying, "It is true that there is no truth". Clearly self defeating.
To demand proof for God is like saying, "Prove to me that it is true that there is truth.". Clearly an unreasonable request.
In fact, if you say there is no God, you are denying all truths, because if there is no ultimate reality, there is nothing that makes anything real.
So since there is reality, there must be reality as it truly and ultimately is. This is what God means.
So let it be known that atheism at its core is a denial of reality, and for that reason no argument with the premise "God doesn't exist" can be accepted as even possibly being valid. You can't make claims about reality while simultaneously denying that there is reality.
There is no argument against the ultimate reality.
And this is why it is not written in vain,
"The fool hath said in his heart, There is no God. Corrupt are they, and have done abominable iniquity: there is none that doeth good.
God looked down from heaven upon the children of men, to see if there were any that did understand, that did seek God.
Every one of them is gone back: they are altogether become filthy; there is none that doeth good, no, not one."