In order to interact with a Domain object, you need to hold a reference to it. One way of achieving this is by creation. Alternatively, you can traverse an association. In Object-Oriented programs, objects have links (references) to other objects, which makes them easily traversable, thereby contributing to the expressive power of our models. But here's the catch: you need a mechanism to retrieve the first object, the Aggregate Root.

Repositories act as storage locations, where a retrieved object is returned in the exact same state it was persisted in. In Domain-Driven Design, every Aggregate type typically has a unique associated Repository, which is used for its persistence and fetching needs. However, in the case where it's required to share an Aggregate object hierarchy, the types might share a Repository.

Once you've successfully retrieved the Aggregate from the Repository, every change you make is persisted, which removes the need to go back to the Repository...