The four Gospels do not narrate Jesus's life as a single continuous account: they differ on sequence, on which episodes each includes, and on emphasis, Matthew and Luke opening with birth narratives John does not tell at all, John structuring Jesus's ministry around a different set of journeys to Jerusalem than the other three. A screen dramatization spanning roughly six hours has to resolve those differences into one throughline, and Zeffirelli's screenplay does so by harmonizing rather than choosing a single Gospel to follow, weaving material from all four into continuous scenes.
The clearest sign of that harmonizing work is a character with no Gospel original at all. Zerah, a Temple scribe played by Ian Holm, was invented for the production to give a single face and a continuous motive to the diffuse opposition the Gospels attribute to "the scribes and the Pharisees" as a group; the screenplay uses him to drive Judas's betrayal, turning a theological and political conflict spread across many anonymous figures in the text into one sustained dramatic antagonist. Naming that invention plainly, rather than leaving a viewer to assume every character on screen has a named scriptural counterpart, is the same discipline this atlas applies to The Ten Commandments's own extrabiblical additions.