where did the office of joshua come from in the royal arch and what are his duties

The historical figure of Joshua, son of Josedek the High Priest, originates in the biblical account of the return of the Jews from the Babylonian captivity to Jerusalem under Zerubbabel their prince and Joshua their high priest 2. In the English Royal Arch system, Joshua is represented as one of the Three Principals—designated by the letter J.—where he stands for the High Priest alongside the Prophet Haggai and the King Zerubbabel 2.

As one of the three presiding officers of a Chapter, Joshua wears an official jewel consisting of a Book surrounded by rays of glory within an equilateral triangle 2.

Beyond this administrative role, Wilmshurst reads the character of Joshua symbolically as the personification of the active, executive aspect of spirit 1. Interpreting the name literally as "divine saviour" and his priesthood as a mediatorial link between Deity and human nature, Wilmshurst holds that Joshua represents the functional power within man that works to overcome lower instincts and promote spiritual perfection 1. Together with Haggai and Zerubbabel, this office forms a triad representing the summit of man's spiritual nature acting as a single unity 1.

Haggai originates as the biblical prophet who urged the returning Jewish exiles to rebuild the Temple in Jerusalem. In the English system, Haggai is represented as one of the Three Principals—designated as the Prophet—alongside the King, Zerubbabel, and the Priest, Joshua 2. As one of the presiding officers of a Chapter, Haggai wears an official jewel depicting an All-seeing Eye surrounded by rays of glory within an equilateral triangle 2.

Symbolically, Walter Leslie Wilmshurst interprets Haggai as the passive aspect of the spiritual principle within man, complementing the active executive aspect personified by Joshua 1. Wilmshurst writes that Haggai signifies the blissful, self-contemplative nature of the spirit 1. He holds that the title of "prophet" denotes the power of insight and omniscience that transcends time, projecting spiritual intuitions and foreglimpses into man's lower intelligence 1. He further notes that the name shares its root with the Greek word hagios, meaning holy, representing the state of holiness or wholeness within the individual's spiritual nature 1.