Views are a description of the data(metadata). When a view is a reference in the FROM clause its metadata is retrieved from the system catalog and placed into query. While working with a non-indexed view, the portion of the view is resolved at run time.

In the case of the Index view, the view's result set is materialized immediately and persisted in physical storage in the database. During the run time this materialized storage is used to resolve the query result. Index view is primary created expecting performance improvement from the query which uses that index.