Originally, Tenjin referred to Amatsukami (heavenly gods) as opposed to Kunitsukami (gods of the land), and was not used to indicate a specific god, but after Michizane's death, it was called Karai tenjin (god of fire and thunder) and was connected to the Raijin-shinko Faith, which led to faith in Michizane's divine spirit and being referred to as the Tenjin-shinko Faith.
本来天神とは国津神に対する天津神を指して言う言葉であり特定の神を指していう言葉ではなかったが、道真が死後火雷天神と呼ばれ雷神信仰と結びついたことなどを由来とし、道真の神霊に対する信仰もまた天神信仰と称するようになった。