I've seen Bruce discuss how he was raised Catholic and that much as he may try he can never escape that past. So, the influence of that Catholicism seeps into his writing and into his music. I think Bruce is just such an exquisitely brilliant songwriter that he sometimes uses evocative religious imagery to tell a particular type of story (e.g. Jesus Was an Only Son tells of a mothers love for her son), expresses the difficulties that people face in their lives and their way of facing these difficulties (Badlands, Rocky Ground) or uses such language in a metaphorical sense to express an emotion (I'll Work for Your Love).

In addition gospel music can be rather beautiful and Bruce's musical influences are as wide and varied as can be, so it's only natural that influences of that gospel sound should infiltrate his own.

I've no idea about whether Bruce himself is a theist or an atheist, and if a theist, what kind of Christianity he might subscribe to.