These are words of great propriety, as befitting a devout Christian.
Literal
Truly devout [classical-なる] Christian [subject-が] send, propriety-heavy words [copula-です].
いかにも 'truly, as one would expect.' 敬虔なる uses the classical attributive copula なる (modern な/である). クリスチャン is a loanword. 礼節重き uses the classical attributive form of 重い (重き), giving the sentence an elevated, literary quality throughout.