Why can modern Icelanders read many Icelandic sagas written in Old Norse?

Modern Icelanders are able to read Old Norse sagas without difficulty primarily because Icelandic is the most conservative of the Scandinavian languages, having preserved its classical grammar, vocabulary, and orthography almost intact since the Middle Ages.1

While other Scandinavian languages underwent significant changes—such as the loss of inflection—Icelandic maintained its complex system of three genders, four noun cases, and intricate verb conjugations. This linguistic stability was supported by factors including Iceland's geographic isolation, a scattered population, and a strong tradition of using the language for literary purposes during centuries of foreign rule.1

Although pronunciation has shifted considerably since the classical period, the written language remains remarkably close to its roots. Furthermore, a 19th-century puristic movement ensured that technical and abstract terms were formed from native Icelandic elements rather than foreign borrowings, reinforcing the language's continuity with its historical literary heritage.1