By itself, a shrine has no power or standing - it needs devotees for that. Characters can become devotees of a shrine either by visiting it and devoting themselves or by accepting an invitation from an existing devotee. The only things which can bar someone from becoming a devotee are if they're in a state of sin, if they've been declared anathema to the faith, or if they're already at their limit for devotions. (You're still limited to ten devotions as a maximum.)
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