I think you are fine to keep most of the general themes and substantive motivations the same: firstly, because they were judged good enough to have your application progressed in the past; secondly, because the firm will have no expectations for your fundamental motivations and candidate profile to have drastically changed in the space of one year. However, you also do not want to seem like you are unmotivated to work on improving yourself and your application. As such, I would aim to include any new experiences or achievements that you can. Similarly, I would try to add new insights you have learnt about the firm: for instance, has it worked on any new major deals/cases, or received important market recognition? Adding these points could strengthen your analysis and make your motivations look more persuasive. Finally, review your writing critically to see if there are any potential improvements regarding style: can you express yourself in a a more concise way? can any points be better phrased? should any sentences be shortened? etc.
