If one prays loudly, one obviously does it to strengthen one's own emotional commitment TO the prayer...not so that God can hear it.... How silly can you get as to think someone else would think it's so God can hear it?

And too... one does it to greatly impress the human audience, of course.

I figure that Mr Roberts did it mostly for the latter purpose, but I can't say for sure, because I don't have a window into his soul. Maybe he fully believed in his own prayers. If so, he would speak louder as he got more emotionally intense. That's normal. So it could have been "for real" or it could just have been showmanship or it could have been both.