If we have been Christian for long enough, we probably know the biblical imperative to share the gospel. Whether by word or by deed, we ought to be willing to share our faith with others.

We also, I am sure, all know people who we think that it is simply pointless to share our faith with.

If we feel any guilt about this, then we remember Jesus' command in Matthew 7:6 not to throw our pearls to pigs lest they trample them underfoot, and use this to justify our reluctance.

The problem is that all too often we are far too quick to assign people this label and hide our faith from them. We look at certain friends or co-workers and remark that 'they swore once, they don't seem receptive to the gospel; there's no way I can share my faith with them'.

So, often unwittingly, based on superficial judgements and fear that we will be humiliated, we deny people the chance to hear the gospel and by our own prejudice we mentally exclude them from receiving salvation. Yet God desires that all people be saved and come to a knowledge of the truth.

Most recently for me, these people were those I was working with over the summer. For two months I held the illustrious position of 'valet' at a local car and van hire. This consisted solely of preparing the cars and vans: cleaning them inside and out, and performing damage checks.

The nature of the job – low-paid and long-houred manual work – meant that the overwhelming majority of my co-workers were working class, lived on the 'rough' side of town and received social benefits. They were not the kind of people you would expect to see in church (so exactly the type of people we should long to see in church).

Of course, there is nothing wrong with any of these things and I eventually came to admire and respect many of my colleagues. However, being a posh, church-going, theology-studying Surrey boy, I made – to my great discredit – an initial thoughtless judgment, deciding that they would be largely hostile to faith matters. This did not mean that I was not going to witness as I worked, although it did make me far less open to how God could have used me.

Sadly I think that we can do far more harm than good when we are seen to be forcing our faith upon people. Therefore my intention was not to shove my beliefs in anyone's face, but to quietly and powerfully witness Christ through a humble attitude, determined work ethic and a loving and generous heart. Should any opportunities arise to share my faith – which they did – then I aimed to do so honestly and plainly; not hiding anything, but equally not forcing anything. Nobody particularly seemed to mind.

As expected, I was the butt of many a faith-based joke. That didn't particularly bother me; it helped keep me grounded. As the summer unfolded, I found that this quiet witness – coupled with urgent and earnest prayer – started to pay off. Colleagues who at first seemed rough and insensitive began to open up. Alongside the jokes we were able to talk freely about faith issues, and a comfortable and safe space developed in which people began sharing deeper and more personal life struggles as we worked.

This completely surprised me. To my shame I had put these people in a box. I had resolved to witness as I worked (as I believe each of us should), but I did not expect anything from it. Instead, I became embroiled in a hotbed of religious and spiritual warfare. From those I had already condemned in my mind came some of the most profound interactions I had all summer.

I beheld the love of one particular co-worker for his wife, listening intently as he detailed how she had saved him from alcoholism when he met her. Her love and care for him softened him and gave him a reason to live. He reciprocally channelled all of his energy into loving her. To my amusement, just 20 minutes later I noticed him blatantly checking out the female customer he was serving – who was not his wife! But he nonetheless waxed lyrical about her. Twenty or so years later they are still together and going on strong.

With one of the branch managers I was able to discuss the Bible at length; how it is 'largely true' and is 'one of the most fascinating books in the world'. It was even suggested to me that I write my next essay about how 'even though all the main characters are dead, they are still present with us'. I jokingly offered him a teaching position at university; he politely declined.

It was also my privilege to hear the stories of two other, backslidden colleagues. Both had been through a lot and fallen from faith, although neither had quite given up entirely. The first stopped attending church after the passing of his mother to cancer. He was keen to make some tentative steps back but had never quite got around to it. He had a family to care for and was 'intently focused on not messing that up'.

The second had attended Sunday school as a kid but gradually stopped as he got older. He says he thinks he was only sent there because it was free childcare. Although he personally wasn't a Christian any more, he told me that he didn't mind that I was. I breathed a mental sigh of relief – how glad I was to have his approval of my faith, I whimsically thought to myself.

One of his good friends is a Christian, he told me, and his favourite band also happens to be Christian – he likes them for their lyrics. He was a genuinely lovely bloke and, despite 'not believing', admitted that he always prayed when things got tough because he knew God was the only person he could turn to.

These were simply the tip of the iceberg. By the end of my time working there, I was astounded. Here was a place I had entirely discounted as surely impervious to the gospel. Yet God was working powerfully behind the scenes. I was completely humbled by this, and emphatically reminded that 'the light shines in the darkness, and the darkness has not overcome it'.

But simultaneous to this light shining is a deep incomprehension of it. It is the Lord who saves – not us. Therefore what is sometimes needed is not a further shining of our own light, but a simple pointing to God's light that is already shining. God is moving, because he loves his people and wants them to be saved. Had I not been so quick to judge, perhaps I would have been faster to see this. And had I been faster to see this, then perhaps I could have been better able to help my co-workers make sense of it.

This was an urgent wake-up call for me. The very Jesus who said 'do not throw your pearls to pigs' is the same Jesus who also told us not to judge and who spent his time feasting with sinners. For me to properly follow Christ, I must allow the Cross to smash all of my pretensions to pieces, and repent of my hypocrisy. If God desires that all people be saved, then I must desire that too; and I must not let my own prejudices get in the way.

God's light shines in the darkness and the darkness has not, cannot and willnot overcome it. We Christians need to realise that as much as any non-Christian does.

Archie Catchpole is a student at London School of Theology.