Nothing. I am not defining a specific God. Everyone knows the concept of God, or a Supreme Being, or Higher Power. No specifics are needed in this hypothetical universe. We just transport in our minds to the different parallel universes.
If you can observe it, it is NOT a delusion. We may be unclear on details, but Something is there.
The issue is not what we believe, or even perceive. It is objective reality ..HYPOTHETICAL objective reality, in this case. We transport ourselves to a God made universe, and consider morality under the assumption that this Being embedded it. The, we cross dimensions in our minds, and come to a godless universe, where only naturalism/materialism is in force.
In the God made universe, where morality is embedded by God, the source is clear.
But in an amoral universe of naturalistic randomness, any belief of absolute morality can only be a delusion, with a source of human manipulators.
There can be no other source, even if you speculate that evolution selected this propensity for delusion as a survival trait, which is a very shaky hypothesis, with no evidence.
No, the 'evidence' is that morality can override animal instincts. It is a civilizing trait, that is esteemed universally among humans. But whether it enhances survival, or is a delusion for fools, is dependent on actual reality.