It is impossible to know why Pope Benedict has chosen to abdicate, but two strong reasons suggest themselves and we will soon know which, if either, of them is right.
One is that he is simply getting too ill to carry on. The problem with that suggestion is that long tradition established that a Pope should die in office.
The determination of his predecessor to stay at his post until his last breath is seen variously as heroic and undignified.
Cardinal Sean Brady takes the first view. He said yesterday in Armagh that John Paul II "taught us how to die".
Yet, in apparent contradiction of that approval of the dying in office approach, he praised the humility of Benedict in choosing to go before ill-health made it impossible for him to function.
Clearly, no one in the hierarchy at the moment is unpacking that paradox in public. John Paul, they say, was wonderful in hanging on; Benedict is noble and humble in letting go.
And the Church is accepting unquestioningly that health is at the heart of the decision.
Still, some may consider another possibility. Joseph Ratzinger was the muscle behind John Paul. He has now been Pope himself for seven years and, in stepping down before his successor is chosen, he puts himself in the position to shape and manage yet a third papacy.
It might be cynical and unfeeling to attribute such manipulation of a high office to this one man – especially if the truth is that he is in failing health.
But would his critics see him as unlikely to think so strategically? Would they think it out of character for him to want to shape the Church so directly? They would not.
This was the man who, as head of the Congregation for the Doctrine of the Faith, sought out and expelled some of the great liberal theologians of our time.
He set his doctrinaire approach in action through the first papacy under his management, that of John Paul, and he continued to shape the Church while in office, as one which would follow his lead.
His policing of thought within the Church extended even to having Irish priests silenced for merely discussing reform.
Those priests would say that Pope Benedict is the one who misunderstands the Church; that he is a Pope who has appropriated too much power.
When he was elected in 2005, one Catholic churchman said to me, with a chuckle, "This is undoubtedly the work of the Holy Spirit, for Ratzinger will wreck the Church and we will be able to rebuild it anew."
Could it be that my friend failed to credit just how powerful and manipulative the old Meister could be?
Benedict will not vote for the new Pope, but he has appointed nearly half of the cardinals who will. He has preserved in office men like Sean Brady, who should have resigned in disgrace.
Now Brady is nominally a candidate for the Papacy himself. He blushed at the suggestion that he might be chosen, but he has a vote and it may be one that Benedict trusts will help to shape the Church the way he wants it. Would it be too cynical to wonder if that vote and that docile spirit of conformity is what has preserved Cardinal Brady in office?
What other value was there in preserving him in office, after disclosures that he had sworn abused children to secrecy had damaged his credibility as a man with qualities of leadership such as were needed?
Yesterday in Armagh, Sean Brady emphasised over and over again that preference for continuity with Benedict's work.
I asked him if the cardinals electing a successor would be looking for a man untainted by the abuse scandals and he sidestepped the question. "I hope we will have a successor who will address that problem and the many other problems", like "the tyranny of relativism and the eclipsing of God".
The Pope is understood to be an appointee of the Holy Spirit. The next one will be looking down at a predecessor, similarly blessed with divine favour, strolling the gardens under his window and may wonder how free he is to diverge in his thinking from this man who has shaped the modern Church in its conservative form.
In resigning, Pope Benedict has diminished the drama of his papacy, which was expected to end with a death and with the rallying of the global Church in Rome for the funeral of a man who had understood God's word and conveyed it infallibly.
He must have understood that he was effectively changing the expectations of the whole Church about how a papacy unfolds and how it touches the hearts of millions in its demise.
He has now set a precedent for a more professional Papacy. To insist on dying in office, after this, may seem gratuitous and inconsiderate, whereas before it was an intrinsic part of the sacrifice made by Christ's vicar.
In future, it may not seem to have been a good idea to expend with such a compelling part of the ritual and mythology. Benedict will understand that.
He can only have done this for a good reason. His detractors will worry that he has outfoxed them again.