Seems to me there are three significant areas of divergence:
1) Not a single congressperson declares themselves unaffiliated (i.e. non-religious, agnostic, or atheist), whereas 16.1% of the US population does. That's a huge difference.
2) There are absolutely no Pentecostals in the congress.
3) There are about three to four times more Jews, Presbyterians, and Episcopals in congress than there are in the general population.
None of these divergences surprise me -- in fact, they fit various stereotypes -- but they are significant differences nonetheless.