Robert said
Ancient historians were relatively free to compose speeches of historical figures based at least in part on what they think the person may have or should have said from their own historical, cultural, and political perspective. Sometimes they may have relied on sources, which also had their own perspectives, or they may have overrepresented their access to reliable sources. It’s not always easy to say. A “narrator” should not always be equated with an author. It’s oftentimes more of a term of art, used in interpreting historical or quasi-historical works with novelistic terms borrowed from the analysis of fictional literature. The gospels are a combination of ancient history, ancient art, and ancient theology. Accordingly, modern interpreters of the gospels choose from among a variety of tools and and paradigms of analysis.  

The gospels are a combination of ancient history, ancient art, and ancient theology? The gospels are definitely part fiction; and as such, one can employ omniscient narrator.

Read Plutarch’s histories or the histories of Suetonius, with all of the religious belief with the leaders of the Republic, I have yet to come across an omniscient narrator. Check Plutarch’s history of Sulla. It is not there. Even with Julius Caesar, the augurs and soothsayers at most interpret signs; however, when you get to Virgil, a fiction writer of the poetic epic, The Aeneid, you get dialogue between human and god.