[ To his credit, Castiel follows the digression without missing a step. ]

Originally it was just known as the fifth day from the start of creation and every seventh day after that, but as other, pagan cultures started adopting the seven day week it gained other names. Association with thunder and the solar system's largest gas giant were common themes. The tribes of Northern Europe named the day to honor Thor. Their neighbors to the south favored Zeus. I think the two had some notable early conflict that made a lasting impression on the whole subcontinent. A few other languages chose to call the day after their regents of Jupiter as well.

For me specifically, it's always meant that it was my turn to aid in watching over the passage of souls from Earth to Heaven. It was a duty I enjoyed.