We don't learn the exact cause of his death, but it's implied that he succumbed to illness. The details of his death are briefly mentioned in the novel.
Here's what we know:
* John was a cruel and bullying child. He tormented Jane and displayed violent tendencies.
* He dies before Jane leaves Gateshead. His death is mentioned in passing by Mrs. Reed.
* His death is not elaborated upon. The focus of the novel is on Jane's journey, not John's life or death.
John Reed's death serves a couple of purposes in the story:
* It relieves Jane of her tormentor. His absence allows her to escape the abuse at Gateshead and begin her journey to independence.
* It foreshadows Jane's own experiences with loss and grief. This theme is prominent throughout the novel, particularly after the death of Mr. Rochester's first wife.
While John Reed's death is not a major plot point, it plays a significant role in shaping Jane's early life and her eventual escape from the cruel environment of Gateshead.