A spirit cabinet is one of the many tools that was designed to aid mediums and spiritualist during this time period. The cabinet was a tool inspired by an audience member viewing a medium. At the time, mediums put on quite show. They summoned spirits and made objects move. Lights flashed, ectoplasm was spewed forth in a dazzling proof that ghosts were among us. One audience member was skeptical and indicated that mediums could be using the same slight of hand a magician uses to produce such affects. They said the medium should be bound in a box so they couldn't use slight of hand.
The spirit cabinet was made to accomplish this. During a seance, a medium was bound in the locked cabinet. Once bound within the cabinet, the medium would produce an even more amazing show. Music and light would come from the box. Sometimes ghosts hands would creep out of cracks and crevices.
Of course, in reality, the spirit cabinet made it even easier for the many fraudulent mediums of the time to fake spiritual encounters. Once locked in the box, they could easily escape their bindings and use their hands to manufacture ghostly phenomena. All they had to do was creep back into their bindings to convince the audience that ghosts had filled the room with the paranormal rather than them. Sometimes spirit cabinets were little more than a curtain with a chair behind it that the medium hid behind.
The cabinets many flaws were exposed by stage magicians like Houdini who showed how easy it is to fake the ghostly phenomena from behind a curtain. This was one of the many nails in the spiritualist coffin that proved that most mediums were frauds and that ghosts didn't move furniture or play music on demand.