I was asked this question recently. One of the best answers I have came from Dondi Scumaci:
People do not commit to a manager, they comply with a manager. People make commitments to a leader.
Leadership is all about influence and is not necessarily associated with a formal title or position. A leader engages people so that they follow that leader by employing many characteristics, especially influence. Integrity, respect, buy-in, and empowerment are other critical qualities of a leader. Managers look after tasks, systems and processes. Managers who fail to influence are not leaders, whatever their title. Managers who lack integrity will lose respect and buy-in and will not be influential leaders.
Leaders are dealers in hope (Napoleon Hill).