You may have spotted that the snippet above is not actually Scripture! It’s from a book I’m reading called The Righteous Mind, by Jonathan Haidt.  

Haidt is a social and cultural psychologist, and his book looks at how and why humans make the kind of moral decisions they make.  It’s absolutely fascinating and I’m underlining things on almost every page, and commenting with a ‘wow’ or an ‘oh, I see!’ in the margins.  

He cites lots of experiments that have been conducted by different psychologists trying to see what factors affect our moral judgements.  We might think we consider situations completely rationally, evaluate the rights and wrongs, and come to a conclusion, but over and over and over again Haidt shows that our intuitions form the strongest basis for our decision-making. And these intuitions can be shaped by things we don’t even notice.  

A study conducted at the University of Toronto found that people who washed their hands with soap before filling out a questionnaire have more moralistic responses to questions relating to moral purity than others (p71.  The quote above also references the opposite effect, such as when Lady Macbeth obsessively tries to clean her hands after goading her husband into murdering Duncan –  immorality makes us want to clean ourselves). 

So all those laws in the Bible about cleanliness had another purpose – not only did they actually fight germs and thus preserve health, not only did they symbolise the need for purity in God’s presence, they actually made people value morality more highly, not just intellectually, but on a subconscious, visceral level.  Having clean hands makes you want a clean heart.  Fascinating.  

(He also made an aside in the early pages about biblical laws that seem really bizarre to us, like prohibitions about weaving clothes with different kinds of thread – they are about “keeping categories pure” (p15). I hope he’ll come back to that later, but it seems as though something similar is happening there – by keeping categories pure in one area of life, perhaps you ‘tune’ your moral intuition to want to keep them pure in other areas, and thus avoid intermarriage with other religions, for instance.)