No image evokes the threat of violent fundamentalism more than the crashing of the planes into New York’s Twin Towers on September 11 twenty years ago. When Chief Rabbi Jonathan Sacks visited the site with other religious leaders a few months later, he observed, “Religion is like fire, it warms but it also burns and we are guardians of the flame”.

The attack prompted him to write one of his best-known books, The Dignity of Difference, which was published a year after 9/11. An appeal for tolerance and a critique of religious supremacism, it argued that diversity was part of the order of Creation and no one faith should claim exclusive rights over salvation.

While the book was hailed in the wider world, ironically Rabbi Sacks found himself soon embroiled in controversy within his own community. He was accused by other Orthodox rabbis of having compromised belief in the “absolute truth” of Torah. Rather than risk his message getting lost amid the raucous cries of heresy, he issued a revised edition early the following year with some of the contentious passages modified or excised.

Gone were sentences such as “No one creed has a monopoly on spiritual truth.” Or “Judaism, Christianity and Islam are religions of revelation”.

In the original, he wrote that “God has spoken to mankind in many languages: through Judaism to Jews, Christianity to Christians, Islam to Muslims.” In Dignity mark two, this was replaced by: “As Jews, we believe that God has made a covenant with a singular people but does not exclude the possibility of other peoples, cultures and faiths finding their own relationship with God within the shared framework of the Noahide laws”.

The effect of the row was to put certain ideas beyond the pale, or at least to drive them to the margins of mainstream Orthodoxy. And yet a couple of decades on, it seems that Dignity represents unfinished business, having opened up the question of Judaism’s understanding of other religions.

Every Jewish child learns that Judaism is not the only road to heaven. The righteous of the nations have a share in the world to come, teaches the Talmud. But the Jewish position can still be characterised as a kind of dignity of indifference. Beyond acceptance of the Noahide laws, Judaism is little interested in the doctrines or rites of other faiths.

Our attitude to other religions has been largely influenced by historical experience —of how Jews have been treated under the rule of others. But a mature Jewish theology surely has to ask what is the purpose of other religions, particularly the two other Abrahamic faiths, even if these are questions which do not have ready answers.

Isaiah thought the raison d’être of the Jewish people was to stand as “witnesses” of God’s existence (chapter 43). But if we are talking about the spread of monotheism, judged in terms of sheer numbers, we can hardly avoid acknowledging that both Christianity and Islam have historically been far more successful.

When Rabbi Sacks described Judaism, Christianity and Islam as religions of “revelation”, he may have simply been describing how the three faiths each see themselves rather than suggesting that Judaism sees the other two faiths as such.

But when he wrote that God spoke through Christianity and Islam, he implied they bore some aspect of providence. That does not mean recognising the content of other faiths as wholly “true” but that there is some truth within them.

In his single-volume encylopaedia, The Jewish Religion: A Companion, Rabbi Louis Jacobs put it this way. “Many modern Jews… prefer to adopt the attitude that while there is truth in all religions, there is more truth in Judaism.” For all its vagueness, they see this as “the only reasonable approach to the great mystery of the God whom Judaism brought to the world and who allows other religions apart from Judaism to exist,”

More recently, other rabbis have tried to flesh out a Judaic response to other faiths. In a collection of essays edited last year by Alon Goshen-Gottstein, founder of the Jerusalem-based Elijah Interfaith Institute, some of the contributors turn to ideas adapted from the Chasidic masters.

Rabbi Arthur Green, universalising the thought of the Me’or Einayim (Rabbi Menachem Nochum Twersky of Chernobyl), argues that the aim of religion is to seek da’at, the intimate awareness of the Divine: the formal structures of institutional religion are just the scaffolding to give direction to our inner spiritual quest.

The Meor Einayim’s “essential teachings”, he says, “that God is present in each moment, that cultivating awareness of this is the key purpose of religious life, and that such awareness leads to profound joy, could all seem to work as cross-traditional truths”.

Rabbi Goshen-Gottstein is himself inspired by the Breslav school. Knowledge of “ultimate truth” is reserved only for a small number of mystical adepts. So faith must come with a humility that acknowledges our limitations, particularly in laying claim to truth. “Even if, in a purely theoretical way, truth is recognised as the ultimate virtue,” he writes, “because it is inaccessible, it must be balanced by the moral and social teaching that privileges peace and tolerance.”

Religious Truth – Towards a Jewish Theology of Religions, edited by Alon Goshen-Gottstein, is published by the Littman Library of Jewish Civilization, £24.95