Mind-Soul Interface

Souls are literally the driving force behind consciousness. Minds consisting of neruons and synapses are still exist in a biological sense. However, there is an additional layer between reality and perception, that being the mind-soul interface. Sensations such as emotions are interpreted by this interface from collections of synapses etc. to Celestial that the soul can understand. This link goes both ways- experiences affecting the soul without a physical counterpart are translated to one's brain. The mechanics of translation are poorly understood, especially when conflicting states are induced- while the overall emotion intensity seems to gradually approach an equilibrium between the two, a level of difficult to quantify 'dissonance' is created which can weaken the interface as a whole in sufficient quantities.
Strong emotions can essentially create a level of 'momentum' that strengthens the bond analogously to a gyrostabilizer. A small consequence of this is that determined individuals tend to survive on their deathbeds for slightly longer.
Celestial (green) quanta interacts directly with the soul. Illusion magic's pain burst spell, for example, pushes the abstract Celestial concept of 'pain' to the target, affecting the soul directly. This is why it works even on entities which cannot feel conventional pain, even those with no nervous systems at all.

MSI & Reality Layer Interaction

When someone sees a Chaotic (red quanta) phenomenon, their physical brain can comprehend it without their consciousness being able to. This often results in seeing things that should be 'impossible': non-euclidean geometry, colors which can't exist etc. The general term for the strange translations from mind to soul are Chaotic Illusions.
However, not all Chaotic Illusions are so out there. Sometimes, it's general concepts which get translated into something visually coherent. For example, Scavengers. Their physical appearances don't make sense: the bone should not be visible from all angles if it's totally covered in shadow. Yet it is.