This is the Imperial Rescript on Education (教育に関する勅語) . Go to Wikipedia for an account of its origin and a translation. It's one of the foundational (if that's a word) documents of the Meiji regime. It's not really "standard" Japanese. It's in highly formalised language, a modified form of Classical Japanese. The putative author (although it was composed by advisers) is the Emperor: the first character is ちん, a first person pronoun used only by the Emperor, and the four kanji below the date (30 October 1890) say "Imperial Signature, Imperial Seal". Language like this was used in formal state documents until fairly recently. Look at the Constitution of 1947, which uses a somewhat less demanding form of it, and although now normally printed with okurigana in hiragana was promulgated with katakana okurigana. Most Japanese people would have difficulty with this text if it was suddenly sprung on them, but many will have studied this particular document to some extent at least in history classes. Fifty years ago everybody over the age of about 35 would have been familiar with it, since up to 1945 it was read daily in schools and displayed on classroom walls. You will often find katakana used for okurigana in scholarly writing by authors of a conservative bent right up to the Pacific War period.