Anglican theologian Austin Farrer coined the phrase "the causal joint" in his book Faith and Speculation and I think it gets to the heart of what I described at the end of the last post. Christian mystery regularly shows up at "the causal joint."
The boundary that was vigilantly policed by Jewish monotheism was between Uncreated Being and created being. To worship created being was idolatrous. Only Uncreated Being, the One who created the universe ex nihilo ("from nothing"), was worthy of devotion and worship. During Second Temple Judaism this contrast between Uncreated and created being encountered Greek philosophical thought which eventually led to the Christian apophatic tradition. While created being is accessible to human observation and exploration, Uncreated Being is an impenetrable mystery. What Uncreated Being "is" in itself is beyond human comprehension.
What, then, happens when Uncreated Being and created being make contact? What is the "casual joint" between God and the world? What does this point of connection and influence look like? How does the Infinite and the finite interact?
As I mentioned at the end of the last post, because one side of the relation is shrouded in apophatic mystery the "casual joint" between God and the world cannot be specified, described, or imagined. At the causal joint we must make an appeal to mystery. This is not done to avoid hard questions or stop the conversation. It concerns, rather, the grammar of God. Due to the asymmetry of being we find at the causal joint no "explanation" can be given for God's relation to and influence upon the world. And the casual joint shows up in a lot of conversations, from miracles, to providence, to prayer. We ask a lot of "how" questions, and "how" questions concern the causal joint.
Basically, mystery evaporates whenever we have a reductive or mechanistic account, if we can specify a causal chain. So we ask questions like "How does prayer work?" or "How do miracles work?" with the expectation that there's some mechanism behind the scenes that we can investigate and uncover. But since things like prayer and miracles show up at the causal joint--the interface between created being and Uncreated being--a mechanism cannot be specified due to the apophatic mystery on one side of the equation. This renders all of God's actions in and on the world inherently mysterious.
At the causal joint, mystery is simply unavoidable.