Not normally used in speech. A more formal, written word for letters and whatnot. Explains the reason for something with the sense that it is precisely because of (person,thing) that( ). 昼間はにぎやかなこの道も、早朝のこととてあたりに犬一匹いなかった。 Because it was early in the morning, there wasn't even a dog around this street that is so lively during the day. 〜のことだから、〜のことなので [kotodakara]
Ref # Kanzen Master Level 1 - p20 - no.19
Often used to give reasons for excuses or apologies.