In a motivation letter it is important to state why you want to work for that specific company. So point out why you want to work for that specific company and not for another company in the same sector? It is also important to state why you want that specific job in M&A/Corporate Finance/Consultancy. You should not summarize your resume in the motivation letter, but further explain why your experience fits the skills needed for this job. Lastly, do not write much more than one A4 page and read your letter multiple times to filter out the spelling mistakes!