When the prodigal son hit rock bottom, he didn't turn to someone familiar or kind. He had to 'glue himself' to a stranger. What does this 'citizen' represent?
The prodigal son sought service not from anyone, but from a 'citizen' of that country. This implies he found himself among people who lived by the world's standards, far removed from his father's household. He had to force himself into service, showing his desperate state and the unappealing nature of his request.
This citizen represents the systems, principles, or even individuals in the world that offer a semblance of support but are ultimately indifferent to our well-being. They might provide a job, a place to stay, or a way to survive, but it's on their terms and for their benefit. They are 'citizens' of a fallen world, operating by its rules, and have no inherent care for the soul.