There is a well known saying that you will never find an atheist in a foxhole. And, I would add, you will never find an atheist in a suicide vest. Most who engage in combat, for whatever cause, are comforted by the conviction that, should they pay the ultimate price, they will be rewarded in the afterlife. In other words, their religious beliefs, if not their rationale for war, provide the courage to participate.
Humans often lean on faith to deal with a variety of struggles in their lives, including illness, addiction and personal loss; of course, the ultimate certainty of death is the primary threat that we all face. Many would argue that religious belief is an essential source of courage, providing emotional support as we endure the many trials and tribulations of life; were it not for the self-delusion and secondary consequences (discrimination, zealotry, anti-science rhetoric) I might agree that religious faith is a benign form of adaptation.
There is another relationship between courage and faith that most humans are unwilling to consider. Immersed in a world of religious conviction and mysticism, the individual is infused with beliefs at an early age and remains under pressure to retain them throughout his life. It takes courage to question the tenants of faith and, in the end, most choose to comply rather than adopt a life of intellectual honesty.