A mother brought her son in to see the doctor. 'Thanks so much for seeing him, doctor', she began. 'The problem is that he's so short. Is there anything you can give him to help him to grow?' The doctor peered over the edge of his large oak desk, looked down at the small boy, and replied to the mother, 'I'm afraid there's not much I can do; he'll just have to be a little patient'.

Readers will now be split into two groups – those who are disappointed because they don't understand the joke, and those who are disappointed because they do understand the joke, but were hoping for a better punchline. The problem for the first group is that explaining jokes, though possible, is often fruitless. As the authors of How to Read the Bible for All its Worth [1] point out, parables are rather like jokes – whilst it is possible to understand them if they are explained to you, they are really something that you need to 'get'.

Parables, like jokes, work by surprise. We're in a familiar situation when something abnormal happens. We are suddenly confronted with a spiritual truth. The problem can sometimes be that many of the situations on which Jesus' parables rely are unfamiliar in modern life. Nowadays they may only bewilder and confuse, rather than shocking, shaming or reassuring as they once did.

Have you ever heard this parable (adapted from a modern version of the good Samaritan found in How to Read the Bible for All its Worth)?

It was a busy Friday evening in the Accident and Emergency department. In one corner of the waiting room sat a scruffy family with frightened children. They had arrived only the previous week from Eastern Europe and were finding life in the UK difficult. Their eldest son had just been beaten up by a gang of racist youths.

A member of the hospital chaplaincy service saw the family, but decided that it probably wasn't worth trying to talk to them since their lack of English would make it such hard work. Besides, he was late going home, so he headed off to the car park. The SHO who saw the boy was an occasional church-goer who sang in the church choir. He felt compassion for the family, but he had been working for six hours already and was just about to get his first break. He rushed through the formalities of history and examination and scuttled off.

The porter wheeling the boy to X-ray was an outspoken atheist, who had never been to church in his life. He chatted to the family, and after his shift was finished, went down to A&E to see if they were still there. They were, so he put them in his car and drove them home, via the supermarket where he bought them a week's supply of shopping. He was round the next day with a bag of clothing and some money to top up their gas meter. He drove the father to the job centre and helped him fill in the forms there. He was off on holiday the next week, so he left them a big roll of bank-notes to keep them going until the father could get a job.

The parable of the good hospital porter: less well known than the parable of the good Samaritan, but pretty effective at surprising us?

The shock in the parable of the good Samaritan,[2] comes when the Samaritan turns up. Jesus told the story in response to a question by a Pharisee that sought to draw attention to his own piety. 'And who is my neighbour?', the Pharisee asked, trying to show everyone how well he was doing in obeying the law that told him to 'love your neighbour as yourself'.[3] Going through the parable, he would have been contemptuous of the priest and the Levite who passed by and ignored the man in the ditch. He could imagine what would happen next. A good, pious Pharisee – just like himself, in fact – would come along and help the man up.

In the parable of the good porter, after the failure of the chaplain and the SHO, were you just waiting for the good CMF member to come along and bail out the poor family? And so the sting. Jesus abolished the Pharisee's question, designed to praise himself and put limits on whom he needed to love. Instead he pointed the spotlight at the Pharisee's own hatred of Samaritans (and contempt towards priests). We are robbed of the chance to congratulate the CMF member, doing what we like to think we would have done in such a situation. We are made to look deep inside at our own attitudes, and at what makes us feel uncomfortable at an atheist doing what a Christian should have.

Chapter eight of How to Read the Bible for All its Worth helped me to take another look at the parables – stories so familiar that they have often lost their power to arrest us. Put yourself in the crowd, and listen to what Jesus has to say. Hear his rebuke to smug Pharisees, but also his reminder to people, like the distraught tax-collector standing in the temple crying for forgiveness,[4] that God doesn't turn away those who sincerely cry out to him.