A well integrated project plan is the primary tool for effective coordination of the work and for tracking and steering progress by appropriate initiatives. It's the key document as a basis of reference. It's like a project bible and is sometimes called the project brief. A project brief may also be required to obtain other approvals such as client commitment to the details, and funding to proceed into subsequent phases of the project-life-cycle.
A good project brief will set out the goals, objectives and scope of the project (its deliverables), how these are to be achieved (technical content), quality (technical standards), any supplementary approvals that may be required (regulatory), design outlines (sketches and block diagrams), the component parts (breakdown structure), who will be responsible for what (team responsibilities), sequence and timing (logic network and schedule), required budget (supporting cost estimate), resources required for implementation (human and material), other resources (space, existing assets, external interfacing), financial considerations (economics and cash flow projections), justification (the impacts and alternatives), and areas of uncertainty (risk), contingency and control plans.
Goals and objectives, by the way, are sometimes used interchangeably but really a goal is an overview statement while an objective is one of the components or stepping stones of which the goal is comprised