This is a pilgrimage offering from the 1456 Holy Year of Compostela made by "Johanes Gudguar" (thought to be the English priest John Goodyear) and recorded in the cartulary known as "Tumbo F" of the Santiago Cathedral.
The altarpiece has 5 alabaster panels that depict episodes in the life of Saint James the Great: his vocation, mission, preaching, martyrdom, and the transferral of his body. This can be seen from the Latin inscribed in gothic characters at the bottom of the wooden structure housing the panels. Each panel is topped with openwork cresting featuring sharp gables.
The reliefs are arranged symmetrically, highlighting the central one showing the "Preaching in Hispania" scene, indicating that they should be viewed from left to right, in chronological order.
This type of devotional piece was relatively common at the time, and their production was centered on Nottingham between 1340 and 1540. The city's craft workshops functioned as something of a production line, churning out models, narrative resources, iconographic motifs, etc.