On the night of August 11 last year, University of London lecturer Paul Kohler was attacked in his home by four Polish burglars and beaten so badly he was unrecognisable. His wife Samantha was in the house and was also threatened.

Two of the four were sentenced to 19 years each in prison, the other two to 13 years. Speaking after the sentencing in January, Kohler said he would consider forgiving his attackers if they showed true remorse. "Me and my family feel the same way – unless you have the capacity to forgive you can only get more embittered by it.

"That's not to say we are going to forgive straight away. And I saw no sense of remorse from the dock today, nobody would meet my eye."

Nearly a year later, though, it's a different story. Kohler, with his wife and four daughters, met Mariusz Tomaszewski, serving 19 years, at the prisoner's own request and under the auspices of restorative justice charity Why Me?

He told the Mirror: "He didn't try and minimise what he had done. He said he was very sorry, was aware he had fallen from grace, and was aware of his weaknesses. He said he would do his utmost not to do it again, and I felt he was genuinely remorseful and reflective."

At the end of the meeting the family shook hands with Tomaszewski and Kohler says he has forgiven him: "From the meeting I have learned that forgiving is more rewarding for the forgiver than the forgiven," he said. "I had gone to help myself and my family, but in doing so I think we helped him, too."

Kohler gives no hint in his interviews that his forgiveness is motivated by religious faith. That's rather helpful, in fact: Christians are sometimes prone to draw a straight-line connection between Jesus' injunction to forgive and our duty to do so, as though we're the only people capable of such a gesture – and as though it's easy.

In fact, forgiveness is a human capacity, a function of the common grace with which God has endowed everyone. We don't have to hold on to our bitterness and resentment; we can let it go. Projects such as Why me?, which facilitated Kohler's meeting with Tomaszewski, and The Forgiveness Project, which collects stories of forgiveness from around the world, testify to this universality.

Forgiveness can be a liberating and fulfilling experience. But it can be really, really hard – so hard that the pastors and teachers who tell us that it's our Christian duty to forgive can be guilty of serious spiritual abuse.

The Church can ask too much of us.

Forgiveness doesn't mean friendship. If someone has deeply hurt or offended us, we may be able to forgive them. In a church context, that might mean we can share communion with them. Maybe if we've previously been friends, that friendship might grow back. But sometimes church leaders place burdens on members of their congregations that are impossible for them to bear, because they ask things of them that Jesus never asked.

And part of the problem is that church leaders desire to create the perfect congregation, in which that peace, harmony and good fellowship are normal. Anything that doesn't fit the norm is frowned upon. So people who've been hurt can come under tremendous pressure to make light of what's been done to them, to pretend that they're 'over it' and to wear the mask of friendliness no matter how much it costs them.

In the wrong hands, the doctrine of forgiveness can be a deadly weapon, allowing evildoers not only to escape the consequences of their actions but to inflict even more damage. It's common to find stories of woman who've been subjected to physical or emotional abuse and been urged to "forgive" their attacker by well-meaning but dangerously uninformed pastors. We need to probe much more deeply into what forgiveness looks like when the power relationships are so unequal; when the person who's done wrong doesn't think they have, or when they take forgiveness for granted, or when they repeatedly abuse the gift that's offered.

When Peter asked Jesus how many times he should forgive – seven times? Jesus answers, "I tell you, not seven times, but seventy-seven times" (Matthew 18: 21-22).

We assume that Jesus means 77 separate offences. It's an extreme way of saying that there's no limit to the number of times we ought to forgive.

But maybe he's also acknowledging that there's no limit to the number of times we might have to forgive the same offence. What has been done to us keeps coming back: the memory of injury or betray rises in our minds again, for the second or the tenth or the fiftieth time, and each recollection requires a fresh act of forgiveness.

At its most fundamental level, forgiveness means setting aside a desire for revenge. Christians are called to forgive and there's no way round that, no matter how hard it is. That's a starting point. We're also called to love our enemies. But that's involves a spiritual journey which we have to make for ourselves; it's not someone else's responsibility to tell us how we should think or feel.

Forgiveness can be a wonderful, liberating experience, as Paul Kohler found. But being asked to give too much, before we're ready to do so, can have terrible spiritual consequences. Forgiveness is good, but maybe sometimes we need to forgive ourselves for not being as forgiving as other people say we should be.

Follow @RevMarkWoods on Twitter.