What does it prove that Spinoza could proclaim an ontology of absolute causality, overturn moral theology, and remain largely unchallenged on the status of causality itself until Hume and Kant forced the issue?
It does not prove stupidity. That explanation would be lazy and self-congratulatory. It also does not prove religious blindness in the simple sense. The real answer is more structural and more uncomfortable. It proves that pre-critical thought had no concept of cognition as a constraint.
Before Hume, “thinking” was assumed to be a transparent medium. Ideas were pictures of reality, intellect was a window, reason tracked being. Errors were mistakes within thinking, not limits of thinking. In that framework, asking whether causality belongs to the world or to cognition is literally unthinkable. It’s not that they failed to ask the question; the conceptual slot for the question did not exist.
Spinoza’s revolution worked only because of that background assumption. He could explain “to the top” because no one yet suspected that the ladder itself might be human-made. His causal necessity felt like an exposure of reality because everyone already assumed that reason maps being. Under those conditions, a total explanation had world-overturning power. Theology could be dismantled because metaphysics was still taken as knowledge.
Once Hume breaks that transparency once he says, “you never see necessity”, the ground shifts. Kant completes the break by saying that not only do you not see necessity, you supply it. From that moment on, ontology loses its revolutionary authority. It can still organize thought, but it can no longer claim to legislate reality.