Seven is a sacred number in all religions and basic life. 7 - days of the week, chakras, planets, deadly sins, beatitudes, colours of the rainbow, notes on the music scale, 21 gun salute (7 guns that fire 3 times), phases of the moon and many more.
I believe its origins come from the Old Testament were GOD created the Earth and everything on it in 6 days and rested on the 7th. Making it Gods favorite number b/c of all his wonderful creations and a day of rest. Hence we have 7 days in a week,
Here's to the home team. Up, Up good questions.