As I find myself going deeper down the rabbit hole of miraculous powers in White Star, it becomes even clearer to me that the Star Preacher and the Star Priest will need to be two totally separate classes with two nearly unique sets of miraculous powers.
The Star Preacher would get powers similar to sanctuary, CLW (at a roll of + 1 to the die), protection from evil / enemies, purify food and drink, light, shield (as the magic-user spell - admittedly not in white box), detect evil thoughts, bless, find traps, neutralize poison and the like. Most powers would take a full round to activate, where he goes through a whole bunch of rituals. Non-believers would suspect it's all smoke and mirrors to hide the fact that science is being used. Light to no armor with a limited weapon selection. He's the medic and support for a well rounded party, able to defend his friends while still trying to find an inner peace. God needs him in the universe and wherever he lands there will be broken beings that need to be fixed, physically if not spiritually.
The Star Priest is the clergy that wades into battle. He inspires his troops as much as he puts fear into his enemy. While the appearance of the Star Preacher would generally be subdued, the Star Priest goes over the top. He wants to be seen by both friends and foe. CLW and well as Cause (with a + 1 to the roll when used to cause wounds), darkness, fear, bless / curse, cause poison, locate object, hold person / monster and the like. All weapons and all armor. He's on a mission for the church and the rest of the party is just along for the ride, and if necessary, the sacrifice. The mission can be a long one to complete and even the priest knows not to question the circumstances his god has placed him in.