I think pain is our primary connection to the real world, i.e. the difference between dreaming and being awake (or “woke” ;D). One of the consequences of this is that pain produces fear, fear produces reflection, anticipation, and forethought, these produce causal thinking, and causal thinking produces wisdom…leading inevitably to my pre-existing heuristic that wisdom = pain * IQ. That is, pain is the reason we ask “why” questions.
In a Christian theological context, pain would be our capacity to “hear” messages from God. We could also hear other messages, but we would have this capacity because pain is our reality antenna. So if we presume that God designed life to feel pain (I’m agnostic on this), then this implies that pain exists because God wants to talk to us using objective reality as a medium. I.e. The fear of the Lord is the beginning of knowledge.
I believe philosophy is a behavioral response to existential terror. That terror comes from the understanding that reality is much bigger and more powerful than we are, as artistically expressed by Lovecraft. Now, this calls back to something commonsensical: all creators and artists have a sort of “artistic fingerprint” that exists in all of their work. (In my head I call the common element in a class of objects the “essence” of that class.) If God created reality then everything real would include this common element. So the fear of reality is also the fear of the creator. If we define God as the “aboutness” of existence, then philosophy follows from the pain of existing.