Creating cross-functional and self-organizing Teams is one of the essential elements of building an Agile Organization.
Both aspects require significant effort & focus. These also don't happen naturally, particularly in organizations led with Industrial Age style of organizational structure and management.
Scrum identifies these as essential aspects and recognizes a specific role - Scrum Master. Scrum Master is responsible for helping the team and the organization achieve Self Organization and improve cross-functionality within the team.
In fact, Scrum Guide specifies it as the first aspect of the Scrum Master's service towards the Development Team.
The existence of organizational power and authority significantly limits the potential of self-organization, hence the Scrum Team is designed to not have any organizational authority and power by any of its members.
The Scrum Master doesn't carry any authority and organizational power, as well as commits to serve the Team's agenda.
Any Scrum Master that doesn't explicitly let go of authority and power, and does not commit to serving the team's agenda, would counter to one of the primary purposes of the Scrum Master role.
Such situation is not Scrum, as the organization won't fully realize the intended benefits of implementing Scrum.
An Agile Organisation is a learning organisation. The Scrum Master helps the teams with creating, transferring and sharing the knowledge and with inspection and adaptation at regular interval.