Today, Catholic and Anglican churches fondly remember Anselm of Canterbury, who is said to have died on April 21 in 1109. But evangelicals are wise to remember him this day, as well.

For those who can harken back to their intro to philosophy class, they will remember Anselm for his mind-boggling proof for the existence of God—(1) God with the property of existence is greater than a God lacking the property of existence. Therefore, (2) because God is that which nothing greater can be conceived, God must possess existence. Though criticized as a mere word game by some philosophers, others have defended it vigorously, the most famous "recent" defense being that of Karl Barth's 1921 Fides Quaruns Intellectum.

Evangelicals are deeply in debt to Anselm for something else—though most are unaware of it. It was Anselm who clearly articulated in theological terms the biblical doctrine of the Atonement known as the satisfaction theory: Man's sin against God demands a payment or satisfaction. Fallen man is incapable of making adequate satisfaction, and so God took on human nature in Christ so that a perfect man might make perfect satisfaction and so restore the human race.

Though this is only one of three major theories of atonement alluded to in the New Testament (ransom and exemplary would be the other two), this theory has become the fundamental or, among some evangelicals—who refer to it as "substitutionary atonement"— the only theory worth bothering about. It is certainly the root theology behind most evangelical preaching about the Cross—thanks to Anselm.

But events of the last few days—with the ascendancy of Benedict XVI to the papacy—bring Anselm to mind as well. Another legacy of this brilliant medieval theologian was his able defense of the filioque, that little phrase in the Nicene Creed that has had such enormous consequences.

The phrase "and the Son" was not in the original Nicene Creed, affirmed officially at the Council of Constantinople in 381. The original read simply that the Holy Spirit "proceeded from the Father." Within a few centuries, Western theologians began inserting the phrase "and the son" (filioque is Latin for "son") into the Creed at this point to battle a theological heresy too complex to go into here.

Since the Creed was considered a formulation of the whole church, agreed together by ecumenical council, the Eastern church was furious with the West's unilateral change to the Creed. They had theological concerns as well—again too complex for this short piece. At any event, this little phrase became one significant cause for the Great Schism of 1054, the first great break in Christendom.

Enter Anselm, who is also known for his able defense of the filioque at the Council of Bari in 1098, which only hardened the Catholic's church commitment to the phrase—making reconciliation with Orthodox even more difficult. That unfortunately legacy has lasted 900 years.

Now enter Pope Benedict XVI, formerly known as Joseph Cardinal Ratzinger. It was Ratzinger who crafted one of his most controversial documents of John Paul II's pontificate, Dominus Iesus (2000). It has been criticized by Orthodox and Protestants as setting back the cause of ecumenism because of its supposedly intractable belief in the supremacy of Roman Catholicism.

But a little-recognized phrase—or the lack thereof—in the document reveals a subtext that drove both Pope John Paul II and now seems to be driving Benedict XVI. Dominus Iesus begins with a restatement of the "fundamental contents of the profession of the Christian faith." Then follows a restatement of the Nicene Creed.

Without the filioque.

The supposedly dogmatic, narrow-minded, intractable Ratzinger (at least according to many a press report) has in some sense already waved the white flag in this battleground between Orthodox and Catholics. When in his first speech as Benedict XVI he said, "The current Successor assumes as his primary commitment that of working tirelessly towards the reconstitution of the full and visible unity of all Christ's followers," he seems to be reiterating something he's already been working on.

He continued, "This is his ambition, this is his compelling duty. He is aware that to do so, expressions of good feelings are not enough. Concrete gestures are required to penetrate souls and move consciences, encouraging everyone to that interior conversion which is the basis for all progress on the road of ecumenism."

Relenting on the filioque in a document like this is not a definitive move of Roman Catholicism, and there is still much that separates Orthodoxy and Roman Catholicism. But the 1,000-year dispute about the filioque no longer seems to be at the center of the division.

Thus, Benedict XVI may be more ecumenical than his critics let on, which will likely bode well also for his relations to evangelicals.

Anselm may be turning over in his grave about the filioque, but he surely is happy with the evangelical insistence on substitutionary atonement. As they say, win some, lose some.

Happy Anselm day.

Mark Galli is managing editor of Christianity Today