This was a cause for rejoicing and a “defining moment” in the kingdom’s history, enthused the Saudi UN ambassador, Abdallah al-Mouallimi.

Within hours though, word came from the Saudi capital, Riyadh, to can the celebration. In a step unprecedented since the creation of the UN—of which Saudi Arabia was, incidentally, a founding member—the kingdom declared that it would renounce the Security Council seat. The foreign ministry’s official explanation was turgid and petulant. The council had failed to bring peace to the Middle East, it said, noting in particular Palestine and the continuing civil war in Syria:

Accordingly, the Kingdom of Saudi Arabia, based on its historical responsibilities towards its people, Arab and Islamic nations as well as towards the peoples aspiring for peace and stability all over the world, announces its apology for not accepting membership of the Security Council until the council is reformed and enabled, effectively and practically, to carry out its duties and responsibilities in maintaining international peace and security.

It is hard to understand how Saudi Arabia can expect to advance its ostensibly reformist agenda by shunning engagement with the very institution it claims to want to change. It is also hard to see how the decision squares with the months of lobbying and careful preparation the Saudis had put into their Security Council bid. At least a dozen junior Saudi diplomats, for instance, spent much of the past year training in New York for the expected widened duties of council membership.

The Kremlinesque opacity of decision-making among the Saudi royal family’s elders adds extra spin to the predictable sandstorm of speculation as to the real reasons for the sudden about-face. In no particular order of likelihood or credibility, here are some of the rumoured explanations:

• King Abdullah, now 89, is known for his occasional bursts of frank impatience. Frustration has been building in the kingdom for months, not to say years, over the perceived unreliability of its main ally for the past seven decades, the United States. But two recent straws have broken the camel’s back. The Obama administration’s sudden rapprochement with Iran—a country the Saudis see as a hostile Shia power and their historical rival—risks unravelling years of patient Saudi efforts at sustaining an anti-Iranian front. And America’s shying away from military action to punish the Assad regime in Syria for its use of chemical weapons against civilians represents a possibly fatal fumble for the anti-regime team that Saudi Arabia strongly backs. Not only did the pro-rebel allies lose a golden opportunity to deliver a death-blow to Mr Assad, as the Saudis see it. American cowardice has legitimised the narrative of al-Qaeda-style radicals, who now threaten to take over the whole of the armed opposition force whose moderate wing the Saudis have assiduously—and expensively—cultivated.

• The decision to reject Security Council membership may not simply reflect an angry fit of kingly pique, however. Saudi Arabia has always preferred closed-doors diplomacy to open forums. A seat on the UN council would have risked exposing, repeatedly and in full public view, the widening policy gap between the kingdom and its closest ally. This would not only represent a break with tradition, but could amount to a strategic mistake that could prove difficult to correct. As if the secretive Saudis needed reminding of the perils of greater scrutiny, deliberations at another UN body, the Human Rights Council, on October 21st, singled out the kingdom for criticism. Two leading watchdog groups, Human Rights Watch and Amnesty International, submitted excoriating reports, noting the country's failure to address discrimination against women and religious minorities, and persecution of dissidents.

• In another variant on this theory, the Saudi rejection could imply that the kingdom intends not to revert into shyness, but to adopt a more aggressive regional role. By this reasoning the Saudis are not simply throwing up their hands in despair, but acting in anticipation of future clashes with the council, perhaps over Syria and Iran. In recent months, commentators known to express publicly what princes say in private have been hinting at a growing Saudi impatience for a bolder foreign policy.

• Others proffer a very different explanation for the kingdom’s retreat into a snail shell: internal power struggles. Some believe the UN move may have been an attempt to embarrass the suave but gravely ill Prince Saud al-Faisal, who has served as foreign minister since 1975. Perhaps, it is said, this was meant as a last push before his replacement by a recently appointed deputy minister, Prince Abdul Aziz bin Abdullah, who happens to be the king’s son.

• One last rumour suggests that the Saudi move may represent the opening gambit in a strategy to secure a Security Council presence for the Organisation of the Islamic Conference, a 57-nation body heavily dominated by the Saudis, which ostensibly represents the world’s Muslims. Despite obvious merits to the argument that the world’s 1.5 billion Muslims remain woefully unrepresented at the Security Council, how this would work in practice is not at all clear.