A coworker once stated that no one can answer why suffering leads to spirituality. Why did G-d make it that way? S/He could have done something else. Well, we could have been made with three arms, vocal cords that do not allow us to choke or see-it-all Google glasses. We were not. I cannot speak to why it is so but perhaps to the function.
I used to ask my Christian friends why they felt prayer was necessary. If God is omnipotent, omnipresent and omniscient, what is the point of prayer? He knows what you want, what you need etc. So, prayer does what exactly? No one could gave me an answer that wasn't full of hidden I don't knows and evasions. I eventually stopped asking. It just made folks uncomfortable.
A couple of months back during a healing, I found myself standing there doing nothing. The healing was taking place unguided by myself. What am I doing here? I am not necessary to this process. That is when the answer to my old question hit me.
People know when they need some sort of intervention. They light candles, go to a church service, do some hocus pocus or the like. All of these things have an otherworldly or external feel to them. When someone that cares about you prays for you, they are expressing compassion and as much as saying, "We are in this together." We pray for each other because it is an expression of compassion. That compassion allows us to grow closer to our fellow humans. We feel less alone. In short, we are learning to unify with each other, tiny little pieces of G-d, until we learn to unify with the larger whole.
We suffer because we are separated. Prayer and other compassionate acts bring us together and alleviates all sorts of pain. Suffering people gain spiritual success because through their own trials, they learn universal compassion. In that state, Unity permeates their being and we see that as spiritual success.