Hey Sharan,
I agree that this question can sometimes be confusing and leave you wondering if there is a "hidden" question within the question.
I had success with this question when I treated it like a story in a sense. I first described how I first became interested in law (e.g. a specific course at uni, an insight event I attended), then how I developed this interest (e.g., shadowing a solicitor, networking), and finally what my motivations/expectations are for my future career. In this final part, I usually linked my answer to the firm; for example, if I was applying to a commercial law firm, I described my interest in commercial law and backed this up with robust examples of how I have developed and maintained this interest - e.g. attending a firm's open day or completing a commercial law virtual experience program.
In this way, my answers started broadly and became more narrow as the "story" went on.
I hope this gives you some clarity!