If we go back to the Latin origin of the English word "religion" (most accepted root is "religare" - "to bind fast"), it has to do with 'binding fast' to the traditions and practices of a household, including worship of the god held by the householder. Often, rather than being born to a house, one came to the house through being a member of a conquered nation taken as slaves. Too keep "order" in the house, it was essential that all living in the household follow the same practices.
Given that history, and the additional baggage that goes along with "organizationalized" religion today, I must say that I largely disagree with Alan Miller (author of that article). In organizations of all types, today, persons have feelings of powerlessness that threaten the orderly psyches of individuals.
That said, in almost all spiritual traditions, some degree of "relinquishing self" to a power or process greater than the "self" is a central idea. If one is unable to accomplish this to some extent, than the beliefs and practices are rather useless whether one calls them 'spiritual' or 'religious'.