He delivered hundreds of speeches, wrote dozens of books and a mountain of newspaper articles, and appeared frequently on television and radio. But, as Natan Sharansky commented upon his death six years ago this week, Elie Wiesel well understood the power of silence.

This was no contradiction: it was his recognition of the dreadful consequences of silence – forged by his own experience as a Holocaust survivor – that led Mr Wiesel to speak out against gross injustices across the world without fear or favour.

The grim realisation that the world’s silence in the face of the Holocaust did not stem from ignorance shaped his belief “never to be silent whenever wherever human beings endure suffering and humiliation”. “We must take sides,” he declared. “Neutrality helps the oppressor, never the victim. Silence encourages the tormentor, never the tormented. Sometimes we must interfere. When human lives are endangered, when human dignity is in jeopardy, national borders and sensitivities become irrelevant. Wherever men and women are persecuted because of their race, religion, or political views, that place must – at that moment – become the centre of the universe.”

Warning of the “perils of indifference”, as he so memorably put it, was Mr Wiesel’s lifetime’s work. It was the clarity and consistency of his voice which added such power to this message. And its absence is painfully apparent today.

Mr Wiesel was, as the Nobel Committee put it when awarding him its peace prize in 1986, a

“messenger to mankind”.

He was also a fearless messenger to the most powerful of mankind. In 1985, for instance, he used a White House ceremony where he was to receive the Congressional Gold Medal to urge Ronald Reagan not to undertake his planned visit to the Bitburg cemetery in West Germany where several dozen SS men were buried. “That place is not your place, Mr President,” he said. “Your place is with the victims of the SS.” Referencing Mr Reagan’s genuine desire to promote reconciliation as Europe marked the 40th anniversary of VE Day, he continued: “We know there are political and strategic reasons, but this issue … transcends politics and diplomacy. The issue here is not politics but good and evil. And we must never confuse them.”

Eight years later, at the dedication of the US Holocaust Memorial Museum in 1993, he confronted the west’s policy of non-intervention in the civil war in the former Yugoslavia. “Mr. President, I must tell you something,” he said turning to face Bill Clinton. “I have been in the former Yugoslavia last fall. I cannot sleep since what I have seen. As a Jew I am saying that. We must do something to stop the bloodshed in that country.” In time, Mr Clinton did act, while later poignantly noting that it was “Jews of conscience”, like Mr Wiesel, who were the “catalyst to save” Muslims in Europe.

And a further two decades later, Mr Wiesel introduced a speech by Barack Obama at the museum while rebuking world leaders for failing to learn the lessons of the Holocaust. “How is it that Assad is still in power?” he asked. “How is it that the Holocaust’s number one denier, Ahmadinejad, is still a president? He who threatens to use nuclear weapons – to use nuclear weapons – to destroy the Jewish state. Have we not learned? We must. We must know that when evil has power, it is almost too late.” Indeed, despite his closeness to the president, Mr Wiesel repeatedly took aim at the manner in which his administration’s pursued its principal foreign policy goal: securing an agreement with Iran to curtail its nuclear programme.

This willingness to speak truth to power was matched by a refusal to let his message be blunted or perverted by his own political or ideological sympathies. “There is so much injustice and suffering crying out for our attention: victims of hunger, of racism and political persecution – in Chile, for instance, or in Ethiopia – writers and poets, prisoners in so many lands governed by the Left and by the Right,” he suggested in 1986 as he accepted his Nobel Prize. He went on to liken apartheid to antisemitism and decry the “interminable imprisonment” of Nelson Mandela, to speak out on behalf of Solidarity in Poland, and to attack the Soviet Union’s treatment of dissidents and Jews.

The plight of the people of Cambodia under Pol Pot’s murderous regime; the suffering of Iraqis and Kurds under Saddam; the genocide in Darfur – on all of these, and many more, Mr Wiesel demanded action.

As Washington National Cathedral unveiled a stonework likeness honouring Mr Wiesel last autumn, his son, Elisha, provided an important reminder that his father was also an unapologetic and proud Zionist.

“The hardest thing for me is when I come across people who invoke his protests, read his books and cry for the dead Jews — then condemn in unforgiving terms the 6 million Jews living in Israel who refuse to depend ever again on others to rescue them,” he wrote. “So I remind the world that my father didn’t advocate just for the people of Kosovo, Darfur and Cambodia. He also supported Israel and defended her right to exist in peace and security.”

There is little about the state of the world – and America’s role in it – in the six years since his death which would have given Mr Wiesel cause for optimism about the future.

What would he have said about the manner in which Donald Trump callously betrayed the Kurds, the US’ staunch allies in the war against IS, in the autumn of 2019 What would he have made of Joe Biden’s inexcusable abandonment of the people of Afghanistan last summer? And how would he have reacted to the sentiments expressed by far-right Republicans who oppose US military aid to Ukraine? “Let me ask you,” Congresswoman Marjorie Taylor Greene suggested in May. “Has Vladimir Putin stopped his war in Ukraine because of all these sanctions? No, not at all. It hasn’t done anything. So, you know what? I care about our country, United States of America and our people. That’s it.”

We might speculate, too, on how Mr Wiesel would have described those Republicans who have aided and abetted – or remained silent in the face of – Mr Trump’s effort to subvert American democracy. And what would he have thought of Mr Biden’s efforts to negotiate with Iran – despite the regime’s open flouting of the 2015 nuclear accords and continuing support for terrorism, threats against Israel and neo-imperial designs on its regional neighbours?

In truth, we know the answer to these questions. “The issue here is not politics but good and evil,” he would remind us. “And we must never confuse them.”