The three degrees
There are three degrees to which our mental health is affected by our faith - through religiosity, through spirituality and through personal relationship. It's why I believe we have a lot to learn from other faiths, but why I am a Christian at heart - by choice, by faith and by scientific rationale.
The first degree is religiosity. This can be defined as the external appearance of faith - church/mosque/temple attendance, ritual, public liturgy. And it is very useful. There have been over 4000 scientific trials of how practising a faith can improve your health - even more so that stopping smoking and taking pills for cholesterol. In mental health research, there are almost 1000 trials that show similar effects on our mental health. An American psychiatrist, Harold Koenig, has summarised much of the evidence in his Handbook of Mental Health.
However, much of this research was done in the Bible Belt of America and it is hard to distinguish if the effects are due to a genuine faith, or a nominal religious observance. Even so, it is clear that this alone can bring value - being part of a [fairly] functional community, getting out of your house regularly, having a structure to your week and [in some traditions] day. Having a religious system is good for you! But is this because of what you believe or because of what you do?
The second degree is spirituality. This is the internal faith - the beliefs, the goals, the ability to say there is something bigger than us. Again, Koenig's book looks at some of this, showing a preferential health benefit for spirituality over religiosity. For example, psychology research of stress related complaints like eczema show consistently that spirituality is better for you than religiosity.
Ironically, spirituality offers a degree of mental abuse [and hence ill-health] that religiosity does not. A system than [in the name of the spiritual] can induce guilt, sanction oppression and blackmail the faithful. When we get beyond the simple attributes of religious behaviour and into the cognitions of spiritual belief, there is a whole manner of ways in which the belief may be used as much as misused. However, on balance it is still better than religiosity - according to the science.
The third degree is a personal relationship with a living God. Ok, this is something unique to the monotheistic religions [Judaism, Christianity and Islam], but there's not a lot I can do about that. This where I think these faiths differ from others. All faith agree on many things - obvious things like not marrying your sister, not killing people and being kind to others - and less obvious things like a strong tradition of the spiritual life, fasting, community and existentialism. However, they differ on a number of key things - the nature and person of God, where we will spend eternity and the identity of humankind.
It is this last aspect - the unique perspective on the identity of humankind as chosen of God - that I believe has the greatest potential for mental health. OK, there is less science on this one, but there is still psychology, testimony and theology going for it. To know that you have a reason for living above and beyond that of evolution [there is no meaning] and Buddhism [there is only impermanence] answers the craving I believe we all have and need for knowing we have a place in this life. This website is full of testimonies that state the key role this type of faith has played in a return to mental health.
Christianity goes three steps further than any other religion and tells us we are the sons and daughters of God, are loved unconditionally by Him and he is pleased with our very existence - even if we have done nothing of value otherwise [read Luke chapter 4]. This to me is the most amazing thing that can ever be said about mankind, the most empowering, the most health-giving and the most important. It puts us in a place of purpose, of value and acceptance from which we can best negotiate the trials of life and contribute to the society we live in and live for.
Yet, it requires an 'Other' who loves - something only Christianity describes.