The “sclerosis” portion of the MS name deals with scarring. Over time, as the mylein sheath surrounding the nerves is attacked and healed over time, over and over again, scarring in the sheath starts to form which can end up getting so thick that it slows or completely blocks signals trying to go through that particular nerve. Many people with MS over time end up losing the ability to feel certain parts of their body, or lose control of those parts of their body entirely.
There is no known cure, and scientists aren’t completely sure what causes it to begin with. There are of course medications available for people suffering from MS, but the focus is more on slowing the progression of the disease, not stopping it.