what does the keystone symbolise in the mark degree and do writers agree on its meaning

In its primary outward presentation, the keystone functions as the central element of a legend rather than as a standalone symbol 1. Mackey holds that while the keystone carries an interior symbolic meaning referring to a Masonic Covenant—serving a purpose similar to that of the trowel—it attracts attention primarily through the historical narrative preserved in the ceremonial work rather than through direct symbolic instruction 1.

Writers have debated the extent to which pure symbolism operates within these degrees 1. Ragon objected to restricting the designation of symbolic instruction to the Craft degrees, considering it an unfavorable criticism that implied the capitular degrees lacked symbolic character altogether 1. Mackey responds that the distinction is one of degree rather than exclusion: while symbols like the keystone are present, the primary characteristic of these degrees remains the preservation of historical tradition and legend, whose interior sense the candidate is left to discern 1.

Albert C. Mackey draws the explicit comparison between the keystone and the trowel as both serving as symbols that refer to a Masonic Covenant 1. The historical origin of the degree's broader stone symbolism, however, is attributed by F. Yates to Thomas Smith Webb, who introduced the symbolism of the rejected stone into his ritual working from an unrecorded source 1.

Scripturally, the association of the keystone with a white stone bearing a new name derives from Revelation 3:17 1. The broader symbolism draws on the ancient practice of the tessera hospitalis, a stone divided between friends to preserve fellowship, and the ancient usage of white stones to signify acquittal, victory, or the bestowing of honors 1.