When something happens or is felt sorely, it occurs in an intense way. If you sorely miss your best friend after he moves to Hong Kong, you miss him a whole lot.
You can say that assistance is sorely needed if your car breaks down by the side of the road, and if your grandparents' old farm house is starting to sag and lean to one side after years of not being cared for, you can describe it as sorely neglected. The adverb sorely is a bit old fashioned, but it's great for emphasizing the large degree to which something is true.