Every Bishop or Priest who has a "church" has what is known as a Canonical Order.

A Canonical order is just the supporting cast of Deacons/Priests who assist the Bishop in the diocese. The type of Priest who might have a Canonical order would be a parson, or a provost.

Once a Friar achieves the rank of Priest, he or she may either remain in the Order, or they may join one of these Canonical orders. Given the nature of our little set up here, Friars will generally end up working for their Bishops, or a Priest within their county/shire.
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In real-life, Friars generally don't aspire to be Priests. There are a few who do become Priests, but this is not why they join an Order. Those looking to be Priests generally join a seminary.

The only thing I can think to compare this to is enlisting in the military, and then going through OTS to become an officer as compared to going through OTS directly.