There's a church in Sydney, Australia, that's been taken to court by a Japanese community leader because he objects to a memorial in its grounds.

It was imported from Korea, and it depicts a seated woman. She represents the estimated 200,000 Korean women forced to service Japanese soldiers as sex slaves during World War II – the Japanese prefer the euphemism "comfort women". According to Tetsuhide Yamaoka, president of the Australia-Japan Community Network, it is "a huge intimidation to Japanese nationals". The church's minister, Bill Crews, has declined to move it. "I find it very sad," he said of the complaint. "To me, it's about the suffering of the women. I've got no antipathy toward the Japanese people."

It's a small story with a huge hinterland. It speaks of one of the Church's heaviest responsibilities: to be a keeper of memories and a witness to truth. People don't always like it.

Japan's relationship to its World War II history has always been conflicted and unsatisfactory. It was responsible for horrific crimes – torture, murder, chemical experiments on prisoners, vivisection, mass rapes – the whole gamut of war crimes. But though its premiers have made repeated apologies to the nations involved, they have never carried the conviction of Germany's acknowledgment of similar wickedness.

One of the reasons for this is the widespread ignorance of modern history among Japan's post-war generations. It is not taught, and they don't know what happened. In an article in the Review of Japanese Culture and Society, 'The Logic of Apologizing for War Crimes "as a Japanese"', Bessho Yoshimi and Hasegawa Eiko describe the grief and horror of a Japanese student in America confronted with the truth. He felt he had to take on responsibility for it because of his nationality; he had never been given the opportunity to process it before.

The Church is there to speak the truth. In Japan, it is numerically weak. But in 1966, on the 25th anniversary of the founding of the United Church of Christ in Japan (UCCJ), it issued a statement confessing its part in the sins of the nation: "Indeed, even as our country committed sin, so we too, as a church, fell into the same sin. We neglected to perform our mission as a 'watchman'."

The UCCJ's reflections are clear-sighted. It says: "The Church, as 'the light of the world' and as 'the salt of the earth', should not have aligned itself with that war effort. Love of country should, rather, have led Christians to exercise a rightful judgment, based on Christian conscience, toward the course our nation pursued."

This is what the Church does, and it's a reminder that's needed now as much as ever. It is located within nations, but it stands aside from nationalism. It doesn't align itself with a programme or a party. It judges the world by the standards of the Kingdom of Heaven, and if it fails to do so it falls under judgment itself. That is what happened in Germany and Japan during the war. But it happened in Britain, too, as the Church – with the notable exception of Bishop George Bell – failed to condemn the bombing of German cities and the deaths of hundreds of thousands of German civilians at Allied hands.

It's easy to forget. Turkey would like to forget the Armenian genocide. Indonesia would like to forget the mass killings of 1965. They must not be allowed to do so. But it's not just ancient history we forget. While the eyes of the world are fixed on Syria, people in South Sudan are facing genocide. While the world frets about Mediterranean migrants, Pakistan is planning to drive back across its northern border three million Afghans and precipitate a humanitarian crisis.

The Church – in the world but not of it, seeking the welfare of the city but an outpost of a different kingdom, a colony of heaven – has a responsibility to the truth. When it backs down for fear of offending the powerful, or attaches itself to their coat-tails for its own advantage, it has failed in its calling to be a watchman.

Follow Mark Woods on Twitter: @RevMarkWoods