Why is physical pain so painful?
I reckon that the reason why physical pain can be so painful is because the Rebel’s karma (‘energy’) is highly concentrated. Normally the pain is insulated from us because it is stored in the energy that composes our bodies (acting like an insulator). But a break in the physical body’s harmony releases the energy/pain.
The energy/pain of the universe is like an exploding atomic bomb that needs to be controlled and diffused, hence us lifeforms who have evolved to act like buffers. The ultimate goal of the Great Work is to create a life form that diffuses the pain/energy/karma to nothing. Think of a stone creating ripples in water. The ripples look similar to each other but get smaller and less energetic (i.e. holographic) as they spread away from the initial impact. The planets are similar ‘ripples’ spreading away from the highly energetic central sun.
To defeat pain/karma, you have to become pain/karma. Mind and Matter have to merge in an alchemical union. To explain this, think of a relay runner who matches his/her running speed with the incoming runner so as to avoid a painful collision. The runner mirrors his/her colleague so it seems as if there is only one runner.