Laus deo? On composers' expression of their spirituality

We might assume that composers of previous epochs were deeply religious people - but have we any proof of that? On the other hand the second half of the twentieth century witnessed the rise and rise of the overtly spiritual composer. Postmodern composers after Messaien seem to wear their spirituality on their sleeves. It becomes for them a readily expressed identification tag - a label, for all to see. But is it for real, and can audiences today really empathize with the spiritual in a composer's music or are they only bewitched by the seductive texture, the return of consonance, the almost-singable tune? The reputations of John Taverner, Sofia Gubaidulina, Arvo Pärt, James MacMillan et al. have been built on such as this. Where God is in the midst of such composers, what are the common threads that bind them and how do they understand the nature of their inspiration?