"Thus saith the LORD" is a frequent refrain encountered in the Old Testament of the Christian Bible. The Jews' Torah and Tanakh tells the same story in Hebrew. The thing is, though, that since the earliest primitive religions were recorded, not once has God ever spoken out of his very own Divine mouth for us to hear, it is always men who presume to speak the words of God.
Not all believers in God are mentally ill. But these primitive, self-proclaimed, prophets of God were likely one of two types. (1) Either they were mad, apocalyptic fundamentalist lunatics, who actually believed they were speaking God's words, or (2), some of them knew exactly what they were doing, and pretended to speak for God in order to spiritually and consequently subjugate the people and bend them to their will. Whether a prophet was of the first or second type, his followers were blindly willing to obey his every word without question or hesitation because they believed he spoke the very words of their God.
Whether the prophet was of the first or second type, mad lunatic, or master manipulator, the God they presumed to speak for invariably hated the same peoples and practices that the prophet himself hated. This only strengthens the case against God and consequently strengthens the atheist position. God has never spoken in his own voice, which if a God existed, he could easily do, and in the language of every human on earth simultaneously. These prophets only believed themselves to speak for God or pretended to.
There is no empirical evidence that any supernatural Supreme Being exists. Physicists have several good theories that show that the universe can be timeless and uncreated, none of which violate any known laws of nature or physics. This also strengthens the atheist position, and establishes the likely non-existence of God. And while not all believers are mentally ill, they have foregone the use of their reason, and have been duped into believing the words of the mentally ill and manipulators.