„留学を前に諭吉が二人に念を押したことは、「手紙は毎便必ず出しなさい。用がなければ用がないと書いてよこしなさい」ということでした とはどういう意味ですか?

質問を翻訳

What Yukichi told the two strongly before their deperture for study abroad was that they had to keep Yukichi posted every time. Even when they had nothing to tell him about, they still had to write him to say so.