It's Blue Monday, apparently the most depressing day of the year.

The calculation's made by using facts like debt levels after Christmas (the credit card statements are arriving), the rather grim weather and the failure of most of us to keep our New Year resolutions.

It's a curiously attractive idea. Not all of us are rays of sunshine all the time. My own Twitter bio describes me as "Happy being a grumpy old man" (someone in the office wrote it and I don't know how to change it – hey, she knows me).

What if there really were a way of expressing exactly how unhappy we are at a given moment? Explaining it means we understand it, and understanding something goes a long way toward controlling it. If we know what makes us unhappy, we can stop being unhappy.

Sadly, it's pseudo-science with no more explanatory power than a newspaper horoscope. But we are, as a society, increasingly obsessed with happiness. Prime Minister David Cameron even introduced a Happiness Index measuring the personal well-being of the nation rather than its GDP. Last September it showed people in Northern Ireland to be happiest, while the Welsh are the most miserable.

What does it take to make us happy? As huge lottery jackpot wins are in the news – $230 million for US couple John and Lisa Robinson and a paltry £33 million for the UK's David and Carol Martin – you might think that money had something to do with it. Not entirely, though: we need to be able to meet our basic needs, but beyond that the happiness boost from increasing wealth tends to plateau.

According to psychology professor Sonja Lyubomirsky, author of The How of Happiness, about half our happiness is what we're born with – some people are just naturally happier than others. Life circumstances, including income, account for just 10 per cent of our total reported happiness, leaving a lot to play for.

So what does Christianity have to say about happiness?

If we mean happy as the world means it (actor Bo Derek once claimed: "Whoever said money can't buy happiness simply didn't know where to go shopping"), we're probably asking the wrong question. In fact, Christianity is rather uninterested in happiness, leaving the purveyors of the "God wants you to be happy" gospel rather scrabbling around for scriptures to back them up.

It talks much more about truth, faithfulness, satisfaction and delight. Happiness, it seems, is not the object of desire but the by-product of devotion. When we seek it in possessions and sensual experiences we are looking in the wrong place. If we're satisfied for a few hours, it won't be long before we need another happiness hit.

Christianity is a thoroughly worldly religion. It encourages us to feel at home in the world and to acknowledge Christ in all of it. It is not really a hair-shirt sort of faith, and there is nothing wrong with enjoying life. But we do tend to notice we are happiest when we are doing something for other people, being part of a family or a community and contributing something meaningful to other people's happiness, rather than just buying more stuff for ourselves.

Blue Monday is a fiction. But the idea that we can control our happiness has something going for it, though in a very counter-intuitive sort of way: we don't do it by seeking to be happy, but by seeking to be useful, to God and to other people.

On the other hand: even that is setting our sights fairly low. Christians want something much better than happiness; we want joy. CS Lewis famously defined it as "an unsatisfied desire which is itself more desirable than any other satisfaction". In his autobiographical Surprised by Joy, he compares pleasure and joy, saying: "Joy (in my sense) has indeed one characteristic, and one only, in common with them; the fact that anyone who has experienced it will want it again... I doubt whether anyone who has tasted it would ever, if both were in his power, exchange it for all the pleasures in the world. But then Joy is never in our power and Pleasure often is."

Ecclesiastes 3:11 says that God has "set eternity in the human heart". Our desires for what is out of reach are really desires for Him. Now, says the apostle Paul, "we see only a reflection as in a mirror; then we shall see face to face. Now I know in part; then I shall know fully, even as I am fully known" (1 Cor 13:12).

Next to that, happiness is just a little boring.

Follow Mark Woods on Twitter: @RevMarkWoods