The developers review the backlog and priorities and commit to the sprint goal during sprint planning. It is the single objective for the sprint. The goal allows the developers to focus on the desired outcome of the sprint and gives them the flexibility on how to achieve it. In addition, it encourages the scrum team to work together rather than on separate initiatives.
The sprint goal is added to the sprint backlog. During the sprint, the developers keep the sprint goal in mind. If during the sprint they find that requirements have to change to meet the goal, they bring the concerns to the product owner to review and negotiate the scope of the sprint backlog within the sprint without affecting the sprint goal.