One of the more recent religions to arrived on Trishore, it was developed over years by Mantaten peoples who had arrived here worshipping spirits and elemental forces. Starting initially as simple hunter-gatherers, the Mantaten peoples borrowed heavily from their (at the time) enemies the Sapoy and their religion, Andronism.
The church began with Priests to help and guide the lay people, and a Hierarchy. However, there was also a need to find new converts and to protect the temples, not to mention the gaining of gold and treasure to strengthen the church. So it came to be that a second arm of the church developed, a more "adventuresome" and externally focused branch, known as the Clergy.
Traditionally the Priesthood is the keeper of the Temple, the preacher and minister to the lay-members, while the Clergy is the converter, defender and proselytizer. On both a human and deity level there is often a conflict between the two arms of a Temple, or even for the Lysturgian Gods. Struggles for power and control arise between the human members of the hierarchy. For example, who is really in charge of a Temple, the 9th level "stick-at-home lazy-bones" Priest or the 9th level "gad-about head-bashing" Clergy?
And for the Gods themselves there is conflict. Both Ashnus and Printep like "action" and the Clergy, but would have far fewer worshippers and thus less power overall without a strong Priesthood. The reverse is true for other Gods like Syphide or Legoss. Most Temples, and the Hierarchy overall, tend to tread a middle road, supporting both because both are needed. This friction is never far from the surface however, and the Garong Crusades of the 2900s are proof that it can even escalate into bloodshed.
There is an occasional blurring of the lines between Clergy and Priesthood, but ultimately the lines tend to be fairly steady and both groups have their share of top-notch applicants. However, there are times when the old, retired Clergyman slows down and joins the safer world of the Priesthood, or a young Priestess dons the weapons and tools of the Clergy for a few years to burn off some energy.
Some Gods or Temples go even further, sometimes hiring special Temple Guards (i.e. Fighters, Paladins, Cavaliers, etc.) so that what happens inside the Temple walls is Priesthood "territory", and what happens "in the fields" is Clergy "territory". The Temples to Braccios are most often found doing this. Braccios Temples in the Jade Freehold (Full Chalice) and Endela (Smiling Warrior) even sponsor full Orders to support these forces and provide incentive to these Guard forces.
To an outside observer the differences between Clergy and Priesthood are subtle. The most visible difference is in cases where the Clergy are allowed to wear more or better armor, or use different weapons than their Temple-bound Priest-kin. However, where this is the case, this is usually offset by the Priests having access to greater granted powers than the Clergy, or getting access to those powers at a lower level than their Clergy-kin. It wouldn’t make much sense for the local Priest to clomp around in full plate mail, with great expertise in how to swing a war hammer, but receiving access to Healing spells, or more powerful Weather control much sooner than others does make good sense.