Jesus says a lot of things that everyone can get on board with, regardless of whether they happen to believe that he's the resurrected Son of God. The Golden Rule, the bits about loving your neighbour and putting each other first: all make good sense, and form the foundation of our society at its best. He says quite a few more challenging things, however, and some of them even have his followers scratching their heads. Often we simply skip over these less straightforward verses, the ones where Jesus appears to contradict himself or say something out of character, and as a result they're often both unfamiliar to us, and a bit troubling every time we encounter them.

One good example of this is found in John 20, where the freshly-resurrected Jesus creates all sorts of havoc among his mourning disciples. Not only does he apparently walk through the wall in order to enter their locked room, but he gives them some complicated instructions about their mission in the future. At the end, in verse 23, he says this: 'If you forgive anyone's sins, their sins are forgiven; if you do not forgive them, they are not forgiven.'

I don't know if the disciples struggled with this phrase, but it's certainly a tricky concept for us to get our heads around. Is Jesus really saying that unless – as Jesus followers and Church – we forgive people, they somehow remain unforgiven by God?

I'm pretty confident that he can't mean that. The rest of the Gospels and the writings of the early Church all seem to contradict that idea (as a few examples, 1 John 1:9 says that God forgives our sins when we confess them, as does Colossians 3:13; while Jesus talks about his blood as the source of sin-forgiveness at the Last Supper in Matthew 26:28). So what is Jesus getting at by suggesting that we have the power to forgive sin – or otherwise leave it untreated?

The answer, as is usually the case in Bible study, is found in looking at the phrase in context. When Jesus has appeared to his disciples, he says three things to them, the third of which is this difficult phrase. First, however, he says (in verse 21) 'Peace be with you! As the Father has sent me, I am sending you.' He begins then by telling them that they are about to take his place at the forefront of spreading his message around the world.

Then, slightly strangely if we stop to picture it, he breathes on them and says 'Receive the Holy Spirit.' So after telling them he's sending them out, Jesus now explains that he's giving them the power of God as backing, and a resource on which to draw as they minister around the ancient world.

So when we arrive at this challenging final verse, he's talking about the content of this message that they're being sent to spread in the power of the Holy Spirit. That message is about the forgiveness of sins – about the fact that the worst mistakes you've ever made don't bar you from life in all its fullness. It's the most amazing, life-changing news, and Jesus is relying on his Church to spread it. Essentially he's saying: if the Church I'm building won't spread this news, how are people going to hear it? So this isn't a threat, it's a rallying cry: if you don't tell people this news, they miss out on the liberation of living without the shadow of guilt, and they miss out on the most fantastic sense of hope. He's not warning of some spiritual hocus pocus which means only they can forgive sins, he's adding a sense of urgency to the mission.

Before Jesus came to change the nature of God's relationship with humanity, God's people used high priests as a gateway to speak with him. Jesus death and resurrection change all that, so the idea that he would immediately be restoring a priest-like barrier between God and man simply makes no sense. In John 10:9 Jesus says, 'I am the gate; whoever enters through me will be saved.' There's no confusion there – our inability to forgive someone's has no impact on their eternal destination.

Instead, Jesus is underlining the importance of the forgiveness of sins, and empowering his people to take his incredible offer of liberation far and wide. Just like that offer, this act of empowerment stretches right through history and reaches to us today, and while the Church through the ages might not always have handled it well, Jesus continues to trust us with his message of forgiveness. So to reframe his challenge to the disciples 2,000 years ago for us today: how will our friends, neighbours, school friends and work colleagues hear about it if not through us?

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