There’s no greater horror, no greater sin, no bigger scandal.

But we usually don’t think of Christian disunity as a problem at all.

It may have been a problem in the year 1000 in the Great Schism — but we’ve learned to live with it since then. The Protestant denominations take things too far, multiplying since the Reformation until they have become so numerous today that they are nearly impossible to count.

But for many of us, it can seem almost a positive thing: Why not divide Christians into separate places where each feels comfortable?

What’s so horrific about Christian disunity? The Catechism of the Catholic Church describes the “sin” of disunity and its consequence: “ruptures that wound the unity of Christ’s Body” (No. 817). This is not mere symbolism. The Church is the body of Christ, and it is meant to manifest Christ’s presence in the world. When it cannot do so with credibility, Christ’s mission is seriously impaired.

The consequences of this great sin are with us every day.

Relativism, the conviction that there is no absolute truth, is at the root of many of the rationalizations that form the basis of modern sins. Why shouldn’t I do what I like with whomever I like? What does dishonesty matter if it doesn’t harm anyone and I get what I want? Who’s to say abortion is wrong? When it’s so expensive to keep the elderly alive, why should we?

Only an appeal to an absolute moral order can answer these ques-tions, but modern ears are deaf to those appeals.

There are many reasons for this disconnect in logic. But one of the most important surely must be the relativism that is written into the very heart of our attitude toward God, the creator of truth. We have convinced ourselves that many denominations can equally claim to tell the truth about Christianity, each coming to a different conclusion on this or that aspect of doctrine, and that it’s rude or worse to claim that one is truer than another.

If we can accept directly contradictory statements about the basis of all reality — the reality of God — as equally true, then what, exactly, is the status of truth?

Thus, even in Christian countries, the witness of Christ’s followers is tainted. The problem simply takes on a more toxic form when Christians of different stripes bicker and fight. We are meant to be the light of the world, but instead, we too often give the world an easy excuse for agnosticism about Christ — and comfort for its moral darkness.

Pope Benedict XVI announced from the beginning of his pontificate that he would “work without sparing energies for the reconstitution of the full and visible unity of all the followers of Christ.”

He “truly feels the pain of a weakened witness by Christians before a world urgently in need of divine truth and love,” said Bishop Brian Farrell, secretary of the Pontifical Council for Promoting Christian Unity.

His work of unity began before he became Pope, for insteance in the year 2000 document Dominus Iesus (The Lord Jesus). It clearly defined what unites Christians, what separates them from non-Christians — and what separates them from each other.

But the astounding signs of success we’ve been reporting on in our series on Benedict’s strides toward unity may be attributable to something else.

Pope John Paul II pointed it out in his 1995 encyclical on Christian unity, Ut Unum Sint (That They May Be One).

At the end of the 20th century, a powerful reality has unified Christians, he writes: the unprecedented number of martyrs. Fascist regimes throughout the 20th century, from Mexico to Eastern Europe to China, were not very particular about doctrinal differences in their zeal to stamp out the Christian faith. Orthodox Christians, Catholics and even some Protestant believers were seen as obstacles to the state’s progress, and were targeted for elimination.

“These brothers and sisters of ours, united in the selfless offering of their lives for the Kingdom of God, are the most powerful proof that every factor of division can be transcended and overcome in the total gift of self for the sake of the Gospel,” writes the Pope.

After a century of anti-Christian violence, “believers in Christ, united in fol-lowing in the footsteps of the martyrs, cannot remain divided,” he said.

As the old saying has it, the blood of the martyrs is the seed of Christianity. Pope Benedict’s clarity and zeal for unity will be indispensable tools for unity. But it’s Christ’s prayer “That they may be one,” and the prayers of so many who joined their sacrifices to his, that will make the Church united once again.