When Bob Dylan performed at the Free Trade Hall in Manchester in 1966 on an electric guitar, a member of the audience yelled "Judas!" at him.

In a 1979 edition of the talk show Friday Night, Saturday Morning, John Cleese and Michael Palin were grilled over Monty Python's Life of Brian by Malcolm Muggeridge and the Bishop of Southwark, Mervyn Stockwood. Stockwood ended the debate by dismissively telling the Pythons, "You'll get your 30 pieces of silver."

The Judas Kiss is a 1998 play by David Hare about Oscar Wilde and his young lover Lord Alfred Douglas.

When Lady Macbeth is praising her husband for killing Duncan, she tells him he is as great as Judas Maccabeus. We all know she means Iscariot.

Judas Iscariot betrayed Jesus in the Garden of Gethsemane. He's come to stand for every kind of betrayal. We all know about the 30 pieces of silver, the kiss, the remorse and the grisly end. But when we've put everything we know about Judas together, we're still left with a shadowy figure, whose motives – like his end – are obscure.

So what does the Bible say about Judas? There are 22 references to him.

1. We're told he was one of the original 12 disciples and went around with Jesus for the three years of his ministry.

2. John tells us he was the group's treasurer and used to steal from their common fund (12:6); he also says Judas did not care about the poor.

3. In John 6:71 and 13:36 he's referred to as "son of Simon Iscariot". No one is quite sure what the surname means. It could refer to a village called Kerioth, or it could just mean "city" as it is like the Aramaic word qiryah; perhaps Judas was from Jerusalem and he was being distinguished from his country bumpkin companions.

Iscariot could also be a corruption of the Latin sicarius or 'dagger-man', one of the rebels who terrorised the area during the Roman occupation. This is unlikely, as they didn't appear until a few years after the events of the New Testament. Other theories include a link to the Aramaic word for 'false one' and that Judas was an 'Issacharite', a member of the tribe of Issachar. No one really knows.

Judas is associated with the love of money not just in John's Gospel but in Matthew too. The chief priests paid him 30 pieces of silver to betray Jesus (Matthew 26:14-16).

4. He betrayed Jesus with a kiss (Matthew 26:49, Mark 14:45); in Luke 22:47-48 it reads as though the kiss may not have actually taken place.

5. After Jesus' arrest, Judas repents and tries to return the money to the priests (Matthew 27:3-5). They refuse it, whereupon he throws the money into the Temple and hangs himself. In Acts 1:18 it says he bought a field with the money and fell headlong in it; "his body burst open and all his intestines spilled out". We don't know exactly how he died.

6. John's Gospel shows the most interest in Judas. At the Last Supper, Jesus predicts his betrayal and tells Peter, "It is the one to whom I will give this piece of bread when I have dipped it in the dish" (13:26); he gives it to Judas and "As soon as Judas took the bread, Satan entered into him" (27). He tells Judas, "What you are about to do, do quickly." The section concludes: "As soon as Judas had taken the bread, he went out. And it was night" (30).

7. Luke doesn't mention Judas at the Last Supper. The implication is that he was there with the other disciples and shared in the meal. Matthew has Jesus predicting the betrayal: "The one who has dipped his hand into the bowl with me will betray me. The Son of Man will go just as it is written about him. But woe to that man who betrays the Son of Man! It would be better for him if he had not been born." Judas asks him if he is the one and Jesus says, "You have said so." The NIV translates this as "Yes, it is you", but that's not what the Greek says; it is much more ambiguous, as though Jesus is saying, "It's up to you." Mark has similar words but misses the exchange with Judas.

Yet, when everything we know about Judas has been laid out, we're still none the wiser about why he did what he did, or what the significance of his actions were. Why did he betray Jesus? In John's account, it's purely for money. But throughout Christian history people have felt this is too small a motive for such a great betrayal. Was it, perhaps, that he wanted Jesus to lead a full-scale uprising against Roman rule and got frustrated when he wouldn't? Was it because he was jealous of the 'inner circle' of Peter, James and John? Did he just become tired of his life with a travelling teacher and miracle-worker?

All of these are possible, and none of them is proveable. Perhaps the question is not really very interesting; and trying to narrow his motives down in this way is inherently wrong.

Another question is, what difference did Judas make? Historically, perhaps, not much: the authorities could have picked Jesus up whenever they liked. They didn't actually need Judas to do it. So what, in the story, is he actually for?

One answer is this. Judas gives betrayal a human face. Whatever his motivation, he did it – a real person handed over his leader and friend to be killed.

In his book Judas: The troubling history of the renegade apostle, Peter Stanford notes the contrast between this understanding and Paul's reference in 1 Corinthians 11:23, where writing of the Lord's Supper he just says Jesus "on the night he was betrayed, took bread..." No mention of Judas. In this account, probably written before any of the Gospels, Judas is absent – and the word translated 'betrayed' can just as well be simply 'handed over'.

Stanford says that "as human beings, we are prone to want to attribute guilt and it is usually simpler to lay the blame wholly on an individual rather than balance their guilt with the many factors that lie behind any crime. Black and white answers trump shades of grey every time. It is back to scapegoating."

This scapegoating has been particularly damaging in Judas' case, as he also notes – his love of money has become a stereotype of Jews in general and has fed millenia of anti-Semitism.

But scapegoating works where the person scapegoated – becoming the focus for hostility or blame – is somehow slightly different from us. In the case of Judas, in the Gospels at least, we don't really see that – though over the centuries he's acquired all sorts of characteristics to make him somehow 'other'. In the Gospels, he is ordinary – and that's the point. Judas humanises betrayal. He makes it universal. Any of the disciples could have betrayed Jesus. So could any of us. We aren't let off the hook by thinking he was especially wicked, though he did an especially wicked thing.

Many of us will sing Johann Heerman's famous hymn, Ah, Holy Jesus, probably in its translation by Robert Bridges. One of its verses says:

Who was the guilty? Who brought this upon thee?
Alas, my treason, Jesus, hath undone thee.
'Twas I, Lord Jesus, I it was denied thee:
I crucified thee.

This painful admission of guilt encompasses the betrayal of Judas as well; he went out into the night, and so do we.

Follow Mark Woods on Twitter: @RevMarkWoods