YOU SAID:

We are but imperfect teachers, but we may be forgiven if we have advanced the matter a little, and have done our best.

INTO JAPANESE

不完全な教師がおりますが、我々 我々 は問題を少し進んでいるし、最善を尽くしている場合に許されるかもしれない。

BACK INTO ENGLISH

When doing your best is going a little problem we have is we have an imperfect teacher might be forgiven.