The more interesting question is what kinds of things did me make up? And, more subtly, when he had choices between Bible verses, which ones did he choose? I see five notable results of his discretionary judgments.
There Are Good Jews
Though much attention has focused on the anti-Jewish aspects of the movie, some of Gibson's fabrications actually seemed designed to assuage Jews. The most important is a completely made up scene in which Jesus's Mother Mary awakens with terror, sensing that her son is about to be harmed. "Ma nish tana halaila hazeh," she says -- in Hebrew. "Why is this night different from all other nights?"
This is not just a Jewish phrase, it's one of the few that most American Jews would actually know since it's part of the Passover liturgy. Even Jews who don't know the Talmud from a tallis would recognize these words. The addition makes the point that Jesus's family, and Jesus, really, really were Jewish.
Another instance of a why-cant-we-all-get-along addition comes when the Sanhedrin meets to conspire against Jesus. There, the wicked Jews are challenged by dissidents. "This entire proceeding is an outrage," says one, in a bit of made-up dialogue. "Who called this? Where are the other members of the council?. This is a travesty--a beastly travesty."
These additions try to shift the movie toward being about bad Jews against good Jews, rather than Jews against God.
And There Are Some Really Bad Jews
The biggest villain in the movie is Caiaphas, the Jewish high priest. This is in keeping with all four Gospels. But Gibson certainly throws everything he can at him. One of the other priests, literally hook-nosed, snarls at Jesus; another smashes Jesus in the head. The movie quotes Jesus himself saying that the big culprit is not the Romans but Caiaphas: "You would have no power over me unless it had been given you from above; therefore he who delivered me to you has the greater sin." This passage appears only in the book of John.
All four Gospels also have the Jewish high priests whipping up "the crowd" against Jesus. But it was left to Gibson's imagination to determine the size and emotion of the crowd. He decided to make the crowd pretty big, probably about 150 people cramming the courtyard. All four gospels said the crowd was offered the choice of freeing Jesus or Barrabas, but some passages describe him as a bandit, some as a political rebel and some as a murderer. Gibson chose to make him a murderer and, tellingly, not a political revolutionary but a ghoulish, serial-killer type, making the choice to release him that much more appalling.
Pilate, Pilate, He's Our Man
Given that Christians for the past couple of millennia have been reciting, in the Nicene creed, that "Jesus suffered under Pontius Pilate," it's rather amazing what a stand-up fellow he turns out to be. Some of the Gospels do indicate that he didn't have his heart in crucifying Jesus, but Gibson's Pilate is so statesmanlike he probably could have edged out Kerry in the New Hampshire primary. In one made-up scene, we see Pilate wrestling through the horns of a dilemma. On the one hand, if he kills Jesus, Ceasar might have his head. But if he doesn't, Caiaphas will cause an uprising (actually, Caiaphas probably wanted Jesus dead to avoid a Roman clampdown). What's a procurator to do?
When Jesus and Pilate are having a private conversation, the Roman leader offers him a drink to quench his thirst. When he's disgusted to discover that the crowd, whipped up by Caiaphas, has chosen to free Barrabas over Jesus, he tells the guards to just scourge him but not to kill him. In another Gibson fabrication, Pilate's lieutenant is depicted as showing up during the beatings to chastise the guards for being too rough.
And then there's Mrs. Pilate. The bible has a brief mention of her sending a message "Have nothing to do with this righteous man." Drawing from a 19th-century book detailing a mystic nun's visions, Gibson creates a fully developed character who is an out-and-out Jesus fan. At one point, she surreptitiously scurries off to give Mary and Mary Magdalene fine cloths which they later use to mop up Jesus' blood. You can almost imagine the girls getting together a few months later to commiserate over figs and tea.
What the additions and subjective choices show, then, is that Gibson was probably influenced as much by Hollywood as his father. The good guys have to be really good. The bad guys have to be really bad. This is not a tendency limited to Gibson, of course, but he should have realized that when filming a passion play he had a moral obligation to aim far higher.
The devil character, who at times looks strikingly like Sinead O'Connor (an accident? I think not!) is an effective creation. At one point he/she is carrying a baby, Madonna-like, who turns out to be a creepy bald guy, a sort of demonic Mini-me. After he betrays Jesus, Judas goes crazy and Gibson imagines him seeing children turning into elf-like demons. For a movie producer who likes his villains to be really villainous, the devil is useful to have around. No one will ever accuse you of depicting him in "too black and white" a fashion.
As has often been noted, it's a violent film. But it's not a violent film in a Braveheart sense, where just about any character might be offed at any minute. The violence is focused almost entirely on Jesus. Obviously, the Bible offers no detail about this, so in each case Gibson chooses to make it as gruesome as possible. The Bible says merely that Jesus is scourged; Gibson has him lacerated almost beyond recognition. Catholic tradition says he fell down three times carrying the cross; "The Passion" has him falling down under the weight of the cross several times more. And, of course, the Bible left to our own imaginations what it must have been like to have a nail hammered into your hands and feet. Gibson does not.
Really, the biggest choice Gibson had to make was what to emphasize about Jesus. He could have emphasized his life and his teachings. He could have emphasized the resurrection. He chose to emphasize the suffering. That is all this movie is about. That means that it is limited theologically (there is more to Christianity than that) and cinematically (no narrative arc, for instance). But it does mean that people who have for years believed that Jesus suffered for humanity, will no longer view that as an abstraction. For that reason alone, it is a movie that will have a profound, lasting impact.