You’re not the first! Ritually concealed shoes (sealed in places like walls and ceilings, or up chimneys and beneath floorboards) are found in the Anglophone world more often than you might think, particularly those dating from the eighteenth and nineteenth centuries (although dating an act of concealment based on the dating of an object that may have been produced at an earlier time is difficult), more commonly in the UK than other places. A large number of them are found — like yours — during renovation or building work, because those are the times people actually look into those kinds of concealed places.

If you still have it — especially if you have left the shoe in situ, that is, exactly where you found it — please report your find to the Deliberately Concealed Garments Project, which is an online collection of exactly this kind of discovery. If you can, take photographs of it where you found it and record the details of when and where it was found and what if anything it was found with, as these details can be enormously helpful for scholars looking to work with concealed objects. The Northampton Museum’s Concealed Shoe Index also keeps an online record of concealed shoe finds, and you can report one there as well. The shoe can also be donated to a museum, especially if they already have a collection of similar objects or concealed garments, although some people prefer to keep them where they were found.

As for why it was put into the wall to begin with, we wished we knew more. Despite the number of such finds, ritually concealed footwear isn’t something that ever made it into the written record. What we have to go on, then, is folklore surrounding shoes and concealment and the material objects themselves — although never underestimate the material record, the significance of concealed shoes was only first noticed in the 1950s by the keeper of the Northampton Museum’s Boot and Shoe Collection, who noticed an odd pattern in footwear donations and started to look into these hidden objects more closely. One other major hurdle is simply in finding, identifying, and collecting information about these kinds of objects. To start with, an object that has been purposefully hidden has to be found, which takes some luck to begin with. Then, they are often found damaged because of their concealment/revealing and because they are frequently deposited only when they no longer serve a practical use, i.e. are already in poor condition. Those who find them then have to realize the significance of what they’ve found (very easy to just toss them in the trash), which poses a major problem for getting a full picture of the practice. Good news, you've already figured out that you've got something significant, which is great!

The most common theory on these kinds of concealed shoes is that they functioned to ritually protect the space where they were hidden. Given the obvious lack of practical application for hiding a shoe in a wall for two centuries, a ritual explanation appears most likely, and shoes as objects lend themselves surprisingly well to such uses. As objects, shoes are closely connected to the person who wears them, bearing the marks of their wearer’s feet, and in folklore their material itself is often used as an apotropaic device (one popular story reports that a man once trapped the devil inside a boot). We also have some shoes that have been found as 'families', i.e. we appear to have the shoes of parents and children together in one space. If concealed shoes did function as a protective measure, it makes sense that multiple family members would be ritually represented. Alternatively, it has also been suggested from other concealed object finds that such deposits could be a kind of sacrificial offering when the earth was disturbed for building construction or similar. But in absence of any kind of reported folk beliefs about concealed shoes in particular though, we can’t be entirely sure.

Eastop, Dinah. “Garments Concealed within Buildings: Following the Evidence.” In Physical Evidence for Ritual Acts, Sorcery, and Witchcraft in Christian Britain, edited by Ronald Hutton (Palgrave Macmillan, 2015): 131-146.

Houlbrook, Ceri and Rebecca Shawcross. “Revealing the Ritually Concealed: Custodians, Conservators, and the Concealed Shoe.” Material Religion 14.2 (2018): 163-182.

Swann, June. “Shoes Concealed in Buildings.” In Physical Evidence for Ritual Acts, Sorcery, and Witchcraft in Christian Britain, edited by Ronald Hutton (Palgrave Macmillan, 2015): 118-130.

I'm late to the party here - I had missed this question; excellent response by /u/tinyblondeduckling. The following is an excerpt about a wide variety of hidden objects uncovered by archaeologists working in the Virginia City National Historic Landmark District. The excerpt is an unedited draft from my manuscript, Monumental Lies: Early Nevada Folklore of the Wild West, which is making its first steps in the process toward publication (perhaps in 2023):

Other objects hint at traditions removed from the mining industry but like all artifacts, they can remain stubbornly silent unless coaxed to speak. Altered coins, the skeleton of a small animal, and various items including a boot represent another opportunity to approach beliefs and practices likely implemented in secret. Archaeologists in Virginia City have found these items, placed beneath buildings or inside walls during the nineteenth century. Although they seem to be hidden attempts to increase good fortune, without written clues, all that remains is to surmise their meaning.

Most people who entered the structures would not have known what had been concealed in secluded shadows. Excavations in Virginia City have identified three examples of this practice from the nineteenth century. Because the act of depositing objects was similar, it would be easy to assume that these were expressions of a shared tradition, but this was almost certainly not the case. People worlds apart inhabited the structures, and while they fell upon analogous strategies to manipulate the supernatural, their acts were in response to distinct traditions.

Likely the oldest of these were two altered coins found beneath the floorboards of the Boston Saloon. This property was operated by William A. G. Brown, a freeborn African American native of Massachusetts. He came to Virginia City in roughly 1863 and soon opened a saloon. By 1866, he had moved his business to D Street, across from the community’s most important theater. The coins were likely probably there about the time that Brown occupied the building, but this cannot be certain. He managed his saloon until about 1875, after which it burned. During an excavation in 2000, archaeologists found a dime and a half dollar beneath charred floorboards. Both had been cut and punctured.

Archaeologist Kelly Dixon expertly described the coins as evidence of a magical practice with roots in southern, African American culture, ultimately reaching back to West Africa. The dime, minted between 1853 and 1860 had a hole drilled into it, causing a fracture; the half dollar, bearing the date, 1865, had two punched holes as well as a wide cut from one of the holes to the edge of the coin. There is evidence that they had been heated, perhaps to facilitate these modifications. Although Brown was from New England, most of his patrons were southerners. As is so often the case with archaeology when lacking written records, conjecture must play a factor. Following whatever path, the tradition of altered coins and their placement beneath a structure found its way into practice, hidden by the floorboards of Brown’s Boston Saloon.

Another archaeologist, Jessica Axsom, uncovered the skeleton of a small mammal beneath a foundation stone of a mercantile store in Virginia City’s Chinatown. It appears that the caustic content of the mortar dissolved many of the animal’s delicate bones, for what remained was too decomposed to identify. Nevertheless, the creature was likely to have been a cat or small dog. The foundation was apparently placed there after the 1875 fire. As with the altered coins beneath the Boston Saloon, no records exist to describe what was intended, but the placement of an animal – or its remains – beneath a foundation of a building was a widespread practice typically intended to confer a level of protection on those using the structure.

Within the remains of a doctor’s house, which also served as a private hospital, archaeologist Julie Schablitsky found several items that were either beneath the building or placed within one of its walls. These include a worn, Civil-War-era boot, a padlock, a bottle, some worked leather, and a hat. Here, it is not clear who might have left these objects because the builder and original owners are unknown. The structure was on the western edge of Chinatown, but there is no reason to assume that Chinese Americans lived there. Again, it is likely that the building was constructed after the 1875 fire. Intent is even more difficult to assess in this case, but the placement of these items is, again, consistent with a pervasive practice of attempting to confer good fortune by hiding objects in or beneath a building.

People of diverse backgrounds left these things, responding to folklore common in many cultures, ubiquitous traditions about what could be left within walls or beneath a structure. Although unrelated historically, these practices draw on similar ideas that objects could grant luck to those living or working there. In addition, the effort to conceal these things was not a communal activity. Often, they were concealed secretly, and practices conducted in private are equally hidden from the historical record.