You never forget an intervention from your best friends. I was 21, in my final year at University, and feeling pretty pleased with myself. For the previous year, I had worked my way up the slippery ladder of the student newspaper, and was now sitting at the top of what was admittedly a very small and under-nourished tree. My face was printed on 12,000 copies of what – when I read them back now – were gut-wrenchingly awful weekly editorial columns. People would vaguely recognise me in the student union bars. My relentless pursuit of the editor's job over that last 12 months had paid off... but then, thank goodness for my friends.

Two of them sat me down in a pub in the city centre, and took it in turns to give me both barrels. You've become a horrible person, they said, in a slightly different form of words which I won't republish here. You're self-obsessed, you don't care about anyone else anymore; you're only interested in the paper. They explained, with uncomfortable examples, how I'd relentlessly prioritised the student rag over them; how it seemed that it was all that mattered to me. Becoming a columnist, then a section editor, then finally the top job. Everything had been about that for far too long, and now I'd changed. I would walk around the town, with a smug fixed grin on my face, waving to people who had no idea who I was like a guy who's been hypnotised into thinking he's the Queen. I had changed, and much for the worse.

Thankfully, the wounds of a friend are faithful. I knew in an instant they were right, and as the scales fell from my eyes, I also became immediately aware of what had gone wrong. I had allowed my ambition to outpace my character. I had been ferociously pursuing a goal, without giving any thought to the consequences of doing so.

Ambition can be a bit of an awkward word in Christian circles. We all instinctively gather that it's probably not a virtue, but it's present in most of us to a lesser or greater degree. For some of us, our ambitions stretch to experiencing a good life, with a family, a nice house and a decent holiday every year. For others, it's much more pronounced: we want to reach the highest rung of employment that we possibly can, or see our business grow enormously. This is true outside the context of church, but also within it: some church leaders become obsessed with size and growth, and with the expansion of their own public profile. Largely speaking though, many Christians are in denial about all of this.

The Bible talks a lot about selfish ambition. Jesus famously asks 'what does it profit a man if he gains the whole world but loses his soul' (Luke 9:25) as a warning to those who would chase material accumulation at the expense of all else. Paul tells Timothy 'those who desire to be rich fall into... a snare' (1 Timothy 6:9), while John says that 'all that is in the world – the desires of the flesh and... pride in possessions – is not from the Father but is from the world.' There are clear warnings about ambition that's rooted in the pursuit of wealth and power. In fact, it was one of the key ways in which Satan himself tried to tempt Jesus in the wilderness in Matthew 4, and the reason the devil himself fell, as described in Isaiah 14:12-15.

Yet does that make all forms of ambition bad? There's a form of very unselfish ambition practised by Paul and the other apostles in the New Testament, where they poured everything they had – including their lives – into furthering the gospel. In Romans 15:20, Paul even refers to his 'ambition' to preach where others have not already gone before him. Clearly a relentless desire to share the Good News of Jesus, and to see the church as a whole grow enormously, is not a sin.

So where then is the tipping point between selfish and Godly ambition? How do we discern whether we're at the Wall Street end of the scale, or simply desperate to see good things happen? Can it be bad, for example, to focus all your energies on ending poverty in a particular country, or seeing the maximum number of trafficked people rescued from slavery? Conversely, can it be ok to want your business to grow and flourish? Where's the line?

Of course, there isn't one. Instead, the answer is found in where your heart is (because, as a wise man once said, there your treasure will be also). The question to ask ourselves is why we're pursuing an ambition: is it because we want to see positive change in the world, or because we want to become more wealthy? Is it about making a name for ourselves, or for others? Ultimately ambition is a question of motive.

Churches which want to grow because they see great need in their community, and want to invite others into a glorious mess which might just meet some of those needs, are not displaying selfish ambition. Business owners who want to create employment opportunities and perhaps even solve local, national or global problems, are probably not practising it either. An office worker who aims to become her boss's boss at some point – so that she can improve the awful working conditions that she and her colleagues have to bear – is probably not struggling with an ambition problem.

On the flip side though, churches which want to grow in order to become known, business people who eye relentless growth no matter what the human cost, and workers who are motivated only by the next promotion, may be falling into a trap about which the Bible warns often. This kind of ambition changes us profoundly; causes us to de-prioritise other people, and seek only our own fame and wealth. And the problem is, it sneaks up on us. A little success becomes addictive, causes us to chase some more, and then turns into a mindset that we never saw coming and still can't perceive.

I'm so glad that my friends cared enough about me to pull me aside and shake me. Many other people aren't afforded such a wake-up call. So all of us should take a moment, every so often, to ask whether selfish ambition has taken hold of us. Because even if we can't see it, we can be sure that everyone else around us can.

Martin Saunders is a Contributing Editor for Christian Today and the Deputy CEO of Youthscape. Follow him on Twitter @martinsaunders.