Most dictionaries suggest leadership and management are quite similar - guiding or controlling a group of people to achieve a goal. Most web articles suggest that leadership and management are different, but offer contradictory reasons, such as: leadership inspires, management plans; leaders praise, managers find fault; leaders ask questions, managers give directions; etc. However, the qualities often ascribed to leadership can also apply to managers. There can be good and bad leaders, and there can be good and bad managers.
For leaders and managers to understand what they have to do, and to achieve excellence in doing it, they need to understand the essence of the difference between them. This is a matter of definition - understanding how the roles are different and how they might overlap.