I think what embarrasses you are the strange symbols and some kanji-like letters, and you seem not to be interested in these elements in this text. What you want to know is surely the pure sentences of kanji letters without these strange symbols.
About these symbols, other comments have already mentioned, these are the auxiliary means in order to read Chinese classic texts which are totally different grammatically and syntactically from Japanese.
See this page:https://en.wikipedia.org/wiki/Kanbun
So, what I can help you is the reconstruction of the original text of kanji letters.
By the way, this text is apparently an annotation to the original text of Sun Tsu （孫子）, which is called The Art of War.https://en.wikipedia.org/wiki/The_Art_of_War
I almost agree with the kanji text you show, except one or two points:
The chapter title is ordinarily as follows:用
間第十三 Chapter XIII Use of Spies, or Intelligence and Espionage, and the the following text may be an annotation of some ancient Chinese author (I don’t know who is), and the text you show us may be a manuscript by a Japanese author or scholar in old time added with Japanese auxiliary symbols and katakana characters to make it readable for Japanese readers.(In the use of these symbols, I think I find some ambiguous or obvious errors.)
I frankly admit that some kanji are impossible for me to decipher. My result is as follows. (I used the ordinary kanji 傳（伝） instead of the actual simplified Chinese character 传. I added spaces to make the text easy to see.
曰 間者 因其所指 其所用 異其名 左傳 謂之諜 杜預曰 謂之細作游偵 一之行人 又云枚掠士
左傳 is a famous ancient Chinese book (ordinarily called 春秋左氏伝 しゅんじゅうさしでん in Japanese), therefore, 杜預 may be the name of a book or an author.
I don’t know the word 枚掠, but surely these kanji mean the action of espionage, because 掠 means ordinarily to steal or to act furtively, and it is followed by 士 person.
- 軍中反間 I am not sure this is 軍, but if so it probably means that in army, counter the espinage
- 探伺？代 This ？kanji is not possible for me to decipher either. I guess that 探伺 means to spy and ？代 might mean generation to generation (sleeper).
Anyway, this text of annotation is not interesting. insipid rather, the original Sun Tse text is not only famous but appreciated even today.
I add the pronunciation in my way of the kanbun text.
いわく、かんじゃは そのさすところ そのもちいるところにより そのなを ことにす。 さでんには これを ちょう といい、 とよが いえり これを さいさくゆうてい という。いつ（ひとつ）に こうじんと、 また