This is a slightly longer version of the article that has gone up at the Guardian's Cif belief...

Religious and spiritual sorts tend to bang on about love. God is love, some say. Practice the art of loving-kindness, others commend. And I've found it hard to know what sense to make of these sentiments. They can so easily lose weight and meaning in a thousand repetitions. Or there is the claim that love reveals and is the fundamental truth of reality. What can be made of that in a scientific age?

Then, I started to read up on developmental psychology, whilst writing a book about love. It seems to me that the modern science illuminates the older, religious claims.

Psychologists and psychotherapists as diverse as Jean Piaget and Sigmund Freud, John Bowlby and Donald Winnicott seem to say that we learn about love in roughly three stages. Our first love is narcissistic - not an entirely pleasant thought, though behaving as if we were the only creature of importance in the world is necessary for our early survival. Freud talked of His Majesty the Baby.

Neonates are lovable and tyrannical. Winnicott showed that the good-enough parent is not perfect but is capable of being devoted to their child, especially in the early weeks. The aim is to instill a feeling that life can be trusted because, on the whole, it delivers what the child needs, physically and emotionally. A sense of wellbeing grows in the young body. It provides the basis for the kind of self-love that enables you to get over yourself and feel comfortable in your own skin. The myth of Narcissus conveys a similar insight. The problem the beautiful youth had was not that he loved himself too much, but that he couldn't love himself.

Narcissism might be called the love of one, and love between two follows next. It is a step into the unknown. It's frightening to awaken to the realization that you are dependent upon another - a parent, in the child's case; a partner, in the adult equivalent: romantic love. But the upside is that life expands. To be one of two promises deeper delights and wider horizons than narcissism can embrace.

There is an assumption that dyadic love, also called falling in love, is the pinnacle of lovely experiences. But it is only the midpoint of the story according to developmental psychology. The next step comes with a secure enough attachment, as Bowlby put it. Equipped with such trust, the child is able to explore the world - to take tentative steps away from the cosy twosome.

It can enter what has usefully been called a triangular space. There's me, there's Mum or Dad, and now there's something else - a third dimension known in the reality of siblings, friends, interests, goals, a current of life that runs independently of me, though I'm somehow part of it. Again, taking that step is alarming, possibly traumatic. However, if negotiated OK, life becomes richer again, and more risky, and the individual's perception of reality grows.

So what does this have to do with God and love? Well, first, consider Plato. He argued that love has an epistemological dimension because of the way it draws our perceptions up a ladder of illumination. We find ourselves on one rung, lower down, and spend some time steadying ourselves with the view. Then, having gained our balance, we are inclined to look up. There's another rung, and an urge to step up. It is an unsettling, possibly frightening, experience. It is more comfortable to stay where you are. But with the right support, another view is gained.

The process can repeat itself, Plato proposed, until a moment is reached when the view that appears is nothing less than a beatific vision. It is as if we have momentarily taken in all that life and reality are. Plato called it the beautiful and the true. Believers call it God. The point is that love resources the ascent. It is a dynamic view of love that is remarkably commensurate with developmental psychology.

A second way of thinking about this dynamic is more simply put. At each transition - from one to two, from two to the triangular space - the individual realizes is that love was already there waiting for him or her. Narcissistic self-absorption relaxes with the realization that I am held in the love of another. Lovers move from falling in love to standing in love, to recalled Erich Fromm's phrase.

The life of faith detects that there is a fourth dimension to add to this third, a divine love that is there waiting. It holds all because it is the source of the love that flows through all. Fear and uncertainty do not cease. Human love always feels a bit like that. But faith is the felt sense that love can be trusted because love is, in truth, the ground of reality.