What are the two essential features a SCRUM Team should possess?

To work as a Scrum Master in a professional Agile team, the individual needs to go on a two-day course to learn Agile principles. At the end of his training, the individual will need to show he can be an effective coach, a facilitator of others' contributions to the team, and a servant leader. He must also demonstrate an understanding of the dynamics of team behavior.

The detail of the latter is necessarily sketchy due to time constraints of the course, but a wider knowledge can be gained by studying the psychology of group and particularly team behavior in Organizational Psychology texts.

It should have all competencies needed to accomplish the work without depending on others not part of the team
It should choose how best to accomplish their work, rather than being directed by others outside the team

Scrum Teams are self-organizing and cross-functional. Self-organizing teams choose how best to accomplish their work, rather than being directed by others outside the team. Cross-functional teams have all competencies needed to accomplish the work without depending on others not part of the team.