what is the esoteric relationship between the Craft and Holy Royal Arch?

Under the English Constitution, the Holy Royal Arch forms the crown and completion of the Craft degrees rather than an optional extra degree 1. Gould noted that the esoteric teaching of the Royal Arch was originally linked with Lodge Mastership as the complement of the Master's grade before becoming detached into a separate Chapter degree 12.

Wilmshurst interprets the relationship between the two as a progressive process of spiritual evolution and human regeneration 1. In his view, the Craft degrees provide the necessary preliminary discipline, purification of mind, and mystical death of the self-will 1. The Craft work remains unfinished without the ultimate spiritual attainment foreshadowed in the Royal Arch 1.

Esoterically, this progression marks a structural rearrangement of the candidate's psychical organization 1. In the Craft degrees, the central symbol of the Grand Geometrician shines high above in the Second Degree and as a ray in the East in the Third Degree 1. In the Royal Arch, this Light descends completely to the chequer-work floor of the physical organism, resting at the centre as the focus of the entire organism 1. Wilmshurst reads this descent as the union of Universal and personal consciousness, where the temporal life-principle is superseded by an immortal principle 1.

While the Craft degrees symbolize the candidate's trials, discipline, and self-conquest in the temporal realm, the Royal Arch portrays the final phase of the soul's journey, escaping captivity in "Babylon" to achieve the spiritual state mystically designated as "Jerusalem" 1.