Division in the church has been a problem since its earliest days. There are detailed Biblical accounts of rows over theology, preferences for preachers, deciding what's ethical behaviour, and more.

Two explanations are often given for our disunity. Firstly, truth: that the church must split when a fundamental doctrine of our faith is in danger. And secondly, sin: that human beings are naturally disposed to disagree and argue, and so unfortunately our imperfect world will always have an imperfect, divided church.

Yet, Jesus prayed for us to be united (John 17:21-23). So we should explore our divisions to understand them and address them, wherever possible. While secular psychology is often not seen as a Christian's friend, it has produced some fascinating research into how and why human beings divide with each other. It's worthwhile exploring whether these divisive forces in our psyche are also at work in the body of Christ.

Social psychologist Christena Cleveland decided to do this in her fascinating book: "Disunity in Christ: uncovering the hidden forces that keep us apart" (Inter-Varsity Press). She acknowledges that as a liberal, city-dwelling Christian, she has her own biases against certain "Wrong Christians". The whole book is well worth a read, especially for her work on cross-cultural relations.

Here's some psychological insights into why we divide:

It can be hard work to deal with "difference"

Humans tend to prefer the easier route. We can be biased against a group of people if it's harder to understand them because they're different from us.

To deal with this harder work, we often put people in "boxes"

Our brains are unconsciously a bit lazy, so they categorise people so that we don't have to work too hard to understand them as an individual, especially if they're a bit different. But this can lead to creating small and arbitrary labels such as "Arminian", "liberal," "preppy" or "West Coast", and making generalisations about them that are only partly true, or not fair at all.

We unconsciously prefer the people we identify with - our "ingroup"

There has been a lot of research on ingroup/outgroup bias. We are much more forgiving, caring, and positive towards people who we consider our "ingroup". This can be based on unchangeable factors like race, gender or nationality, but also chosen characteristics like fashion, football team or religion. As well as being biased against them, we tend to see "outgroups" as all the same – the fancy name for this is the "outgroup homogeneity effect" – even though like any group of people, there is a lot of variety between individuals.

Ingroup/outgroup bias can make us want to be different, even when we're not

Even if we're very similar, division itself can make us focus on tiny differences between "us" and "them". Christena gives an example of two "hipster" churches near each other. Although they have the same great graphic design, worship style, young pastors and fair-trade coffee, people emphasise slight differences such as whether one pastor is more handsome than the other church, and then says "we are nothing like them!" If divisive forces are at work between two very similar churches, what does it mean for churches that are quite different, such as Pentecostals and Calvinists?

Group identity boosts our self-esteem

We tend to want to look at the positives of our "ingroup", because it helps to bolster our own self-esteem, also known as "basking in reflected glory". In experiments by the author, if a group had done well on a task, it would more closely identify with that group. If it had done badly, they would distance themselves from it. Sadly this does mean that humans often choose to criticise an outgroup, just to feel better about themselves.

We are biased to think we're the best

The "gold standard effect" is a psychological bias that makes us (often, wrongly) think that our own way of doing things is the best. Otherwise known as pride, I guess.

We also have self-serving biases that can be shown during experiments, and so we rate our own personal performance more highly than we should do. The combination of factors enhances division, according to Christena:

"By thinking highly of ourselves, we naturally think less of others. There might be social problems in the world, but our group is not responsible for them. That other group is the cause of all of the ills. There might be friction within our local community of Christians, but we're innocent. The problem would be solved If the other church would vote differently, or get serious about living the Christian life, or get their theology straight. They need us, but since we're perfect, we don't need them."

So what can we do to reduce division and overcome our bad psychology?

There's plenty of spiritual solutions, such as prayer and applying Scripture to our lives. But psychology gives interesting insights, too:

Self-examination

One way that experiments have shown we can be less divisive is if we are aware of the biases we have, and work to deliberately challenge them. Ask God to reveal them, being aware that many of them are unconscious, just the way our brains are wired.

Consider yourselves part of a larger group

That can be the whole global church, or even just the human race. Even using the word "we" to describe all human beings can help. Look at the church as the global body of Christ. That includes Christians who are very different in musical taste, culture and practice.

Concentrate on what unites us, not what divides us

Another is to focus on the similarities between your ingroup and an outgroup, rather than the differences. Experiments found that when people think of these shared characteristics, they rate an outgroup more positively. Focusing on the common love of Jesus that all Christians share, for example.

Practice empathy

Another helpful tool is to think what it is like in the other person's shoes – or "perspective taking".

Spend more time with people who are different from us

Go to different churches and spend time in different cultures and countries – long enough to get to know people there. When we learn to identify with people who are different to us, we are less likely to treat them as an "outgroup".

Know we are each loved by God and practice self-affirmation

Experiments on "self-affirmation theory" show that we're less inclined to put other people down and/or be defensive about our 'ingroup', if we feel good about ourselves. Knowing who we are in Christ, a loved child of God, is a much better way to feel good about ourselves.

Have a common goal

Work on a co-operative project together with a different church and/or denomination. Working towards a larger goal helps to break down divisions. As the world around us becomes more divided, it's up to us to learn to become peacemakers, both inside and outside the church.