窶ケテ篠行 gongyo is a special term in Buddhism and refers to the recitation of sutra/mantra, according to internet sources.
Sutra/mantra are mainly Sanskrit language and in Japan they use Chinese version i.e. those transcripted into kanji (or Chinese characters).
So it is not ancient Japanese, it is something quite different.
If you're interested in gongyo, you should learn about it.
If you'Re interested in Japanese language (including acient one), you should forget about gongyo.
I've found SGI's site on gongyo, which you might find interesting.