There are a few reasons why purple holds importance during penitential seasons. One reason is the historical signification of royalty. The making of purple dye during ancient times was rare and expensive, therefore it was the mark of someone rich and powerful... someone like a King.

We know during this same time, Israel longed for a messiah. Messiah means anointed one, which is another phrase for king. Israel was without a king and longed for the return of their kingdom.

The purple used throughout this Advent season signifies the coming of the 'One True King'.