Just some thinking (rambling) here …
We know that it’s God’s will that all Christians be unified (Jn 17:11) under the See of Peter (Mt 16:18-19). We also know that for the last 500 years people (to a greater or lesser degree) have worked to bring about this unity (again, to a greater or lesser degree) through dialog and documents stating common ground between those holding opposing views.
Unfortunately for 500 years of work (almost 1000 years if we count the Orthodox) we’ve made more progress in the cosmetic than we have in substance. All the internal effort so far has not been able to overcome the pride and misunderstanding that led to the scandal of a divided Body of Christ.
Could it be possible that Islam has the ability to do from the outside what we have been unable to do from the inside? Is it possible that the inevitable confrontation between Islam and Christianity forces Christian theologians to turn from the current internal arguments such as those of imputed verses infused righteousness, and turn their attention to more basic areas like defending the idea of a Triune God against Islamic charges of polytheism?
I’m not saying theological discussions between Christians are not important of trivial at all, but would forcing all of Christianity’s greatest minds to come together and once again argue that Jesus Christ is fully God and fully man in a less scholastic and more hostile environment be the start of a lasting unity? Would a couple of generations of this result in the forgetting of the prejudices held today between Christians, and allow a view of Church history and Her teaching to shine through in an unbiased and persuasive way?
The last time Jesus’ divinity was challenged to the extent it is today was during the Arian heresy of the 4th century. At that time the Church called the council of Nicea (325) to address the real and pressing danger Arianism posed to the Church and Her understanding of Jesus’ divinity. It was a fight fought with passion on both sides, and at one point Arianism looked as if it may win the fight. But in the end, after the dust settled, the truth God had given to His young Church shone through and the Trinitarian nature of God was upheld, and a universal creed was born.
Would Christianity come together under an attack (physical, political, theological, …) from Islam? The day is coming (my opinion) when radio programs like Catholic Answers will focus more on Islam than they do on Protestants. God has given us a history full of Him bringing the good from the bad. And while ecumenism imposed from the outside is definitely not my first choice, I do recognize that anything is possible.