ROME — Pope Francis praised Jews for keeping their faith despite the Holocaust and other “terrible trials” throughout history, and reaffirmed Judaism as the “holy root” of Christianity.

Francis made the statements in an unprecedented open letter to Eugenio Scalfari, a prominent Italian atheist and founding editor of the liberal newspaper La Repubblica.

The pope’s letter, published on the front page of La Repubblica on Wednesday, came in response to editorials this summer written by Scalfari that had directly addressed the pontiff on issues of faith and religion.

The pope’s reply affirmed the necessity of an open dialogue with nonbelievers that he called “right and proper and precious.”

The pope also responded to Scalfari’s query about “what we should say to our Jewish brothers about the promise made to them by God: Has it all come to nothing?”

“Believe me,” the pope wrote, “this is a question that challenges us radically as Christians, because, with the help of God, especially since Vatican Council II, we have rediscovered that the Jewish people are still for us the holy root from which Jesus germinated.”

The pope said that, particularly through his close ties with Jews in his native Argentina, he had often, in prayer, “also questioned God, especially when my mind went to the memory of the terrible experience of the Shoah.”

He added that: “What I can say to you, with the Apostle Paul, is that God’s fidelity to the close covenant with Israel never failed and that, through the terrible trials of these centuries, the Jews have kept their faith in God. And for this, we shall never be sufficiently grateful to them as Church, but also as humanity.”

By doing so, Francis noted, Jews served as an example for Christians. “Precisely by persevering in the faith of the God of the Covenant,” he said, they “called all, also us Christians, to the fact that we are always waiting, as pilgrims, for the Lord’s return and, therefore, that we must always be open to Him and never take refuge in what we have already attained.”

Earlier this month, Francis wished the Jewish people a happy new year and called for interfaith dialogue between the world’s religious communities and leaders.

He also reiterated a statement made last June, saying “a Christian cannot be an anti-Semite,” and adding that “to be a good Christian it is necessary to understand Jewish history and traditions.”