Seems like it really could be just an Item of Power with some kind of Sponsored Magic. Wouldn't necessarily be very expensive but with magic and the right Apex Skills (shoot for the Wizards trio of Conviction, Discipline, Lore) he could do some impressive feats as spells.
-Water from Rock would be a transformation or conjuration thaumaturgy (or even evothaum)
-Staff into a snake and back would be a veil opposed by Alertness
-Battle of Rephidim could be any number of boost spells on entire zones that the Israelites could tag for bonuses vs to attack the Amaelekites
-Parting the Red Sea is the most impressive, but is basically a big Thaumaturgy boost to Athletics to defeat the Block that is the Red Sea, having it cover everybody in multiple zones, and then last for the time it takes to cover the zones of the Red Sea. Pharoah's army didn't get this bonus, but it makes more sense dramatically to have them get half way across and then drown.
Staff of Moses [-2]
Musts: An Aspect denoting possession of the staff.
Affects: Conviction, Discipline, Lore
It is What It Is -0 (it's a staff, about the size of a man)
Item of Power Rebate +2
Powers:
Sponsored Magic -4 (name it something Yahweh related, come up with appropriate evothaum (could be something miracle related), and come with a sponsor goal)