Lawyers represent clients, and clients will want to know how laws apply to them. To advise a client, a lawyer needs to understand exactly how an abstract rule of law will apply to the very specific situations a client might encounter.
This is more difficult than you might think, in part because a legal rule that sounds definite and clear in the abstract may prove murky in application.
Great lawyers need a vivid imagination; they need to imagine how rules might apply, where they might be unclear, and where they might lead to unexpected outcomes. The case method and the frequent use of hypotheticals will help train your brain to think this way. (Kerr, 2007)
