Well, a number of Bible stories have characters given literal superhuman strength, but as the religion matured superman stories gave way to promises of peace and future rewards. Religion can offer a believer a structured path to acceptance of horrible tragedy or loss. It is not necessarily the best coping method. Very often the religion's promises ring hollow when really faced with suffering or loss.
In my experience, strength comes from the sober yet optimistic recognition that we, and those we love, are here for a little while and then make room for others after us. There is no cosmic conspiracy, no fated destiny, no great injustice in life being transitory. No one has wronged us. No one has robbed us immortality. No one owes me a perfect world. Strength comes from empowerment, and inner peace. Change what we can and accept what we can't. I always thought it ironic that some pray for that very thing.