It is the project itself that links the requirements to the deliverables. All projects consist of a series of tasks for deploying the requirements in some way, and planning consists of planning and scheduling those tasks in time to determine the delivery timescales.
Whether or not the requirements are "allowed" to change, and the acceptable pace of change in a project requirements and scope, will differ from organisation to organisation and from project approach to approach. So it is not possible to answer whether you need to be reviewing requirements- but typically it would not be the Project Manager who has responsibility for reviewing requirements, it would be an ongoing process between the "business" (i.e the customer) and the various team members (i.e. business analysts, requirements analysts etc.) who usually translate customer requirements into deliverable goals and objectives. The Project Manager would facilitate the review process and have some oversight of the review and outcomes, as well as tracking its progress against the planned review tasks.
Requirements Traceability attempts to ensure that for every requirement or goal stated and defined in a project, there is a corresponding set of appropriate activities that deliver that requirement and test it has been delivered accurately. This is usually performed within various documents and allows someone to start with a documented requirement and trace that requirement through various documents (Requirements Spec, Functional Spec, Technical Design Spec, various development artefacts, Test Plans, Test Scripts, UAT Scripts and UAT Signoff etc. etc.). Then by ensuring all requirements are carried through all documents and have demonstrable deliverables, it can be easily demonstrated that a project delivers on its goals and requirements.
