Confusing sentence (~た次第です, passive speech as active, etc)

Question

Note: I sought out uses of 次第 on other posted questions but didn't find anything that fits here.

There's a sentence in the introduction to 日本語文法ハンドブック (a book written for teachers of beginning Japanese grammar):

寺村先生[an esteemed Japanese teacher the author of this book models himself after]は海外技術者研修協会における草創期の日本語教育に全面的に協力され、同協会の日本語教科書編纂にも大きく貢献されましたが、私[the author of this book]は海外技術者研修協会との縁により、また、若き日の寺村先生の講筵に列した者として本書の監修にあたった次第です。

My questions are:

1. The passive voice used for 寺村先生's work doesn't seem to make sense. Is this a case of substituting the active voice for passive as a matter of politeness?

2. What is 講筵's exact definition? It doesn't appear in any dictionary, although several possible meanings are inferred ("mat a teacher would sit on and lecture from")

3. What is the exact translation of ~た次第です here? The closest definition I can find is "reason" or "course of events", similar (I would think) to ~た理由です or ~たわけです. Is ~た次第です an acceptable substitute for these constructions?

Thanks in advance.

Answer 1

Yes to ①; see this question and its answer, for example.

② can be found in a dictionary, as the comment above by snailboat points out.

Here I'll focus on ③: this 次第{しだい}です has the connotation of circumstances. It is a humble/polite form used at the end of an explanation or clarification to an audience of superior(s). Often used in a professional/work setting. For example:

今日は電車が事故により遅れ、このように出社が遅れた次第です。申し訳ありません。

"(The circumstances are that) I arrived here at work this late today as a result of my train being delayed due to an accident. Please accept my apologies."

(Example taken from here.)

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Note though that there also exists a completely different (more common) sentence-ending {X}次第 meaning It is up to {X}. For example:

そのお金をどう使うかは君次第だよ。 "How to spend that money is up to you."