Each has their own spiritual starting point, but what triggers that point, spurs us to move on?
First, I would put 'spiritual starting point' in quotation marks.
Because from a macro view the starting point for all would be the same--participating in the entire evolution of consciousness from rocks to people.
What if we narrow the field to people.
The starting point is the spark of connection to Real Self, of the beginning of an awareness of this connection.
And what activates that spark?
That point becomes a starting point as it begins to become activated through our brushes, accidental or otherwise, with experiencing beyond our usual limits, beyond through who we think we are. Then our life itself becomes the kindling for that spark.