It was a masterpiece of Vatican diplomacy.
In 2003 the European Union was drawing up a new constitution. This offered a unique opportunity to characterise the EU as a Christian club, by including a reference to Europe's Christian roots. But this wouldn't have much chance of success if the EU were already negotiating the membership of an overwhelmingly Muslim country. So the Vatican spoke out in favour of calling the EU's heritage "Christian", which encouraged a number of Catholic-majority countries to rush to support this proposal. And at the same time it tried to get Turkey to delay seeking membership until Christianity could be baked into the EU constitution.
Even the wording was consummate:
♦ First, there's plausible deniability. The Vatican is in favour, it's just that Europeans aren't, and the Church is kindly reminding of that fact, to help them to time their application better.
♦ Next, it presents Turkish "immigration" as an impediment . But by 2001 there were almost two million Turkish citizens in Germany alone. Many of the children of the "guest workers" who'd begun arrivng in 1961 were already training for, or practicing skilled trades and professions. Germany was on the brink of acknowledging that it was indeed an "immigration land" and belatedly trying to make it easier for its Turkish population to acquire German citizenship. The Vatican itself may have been "not yet ready", but even Germany was rapidly becoming so.
♦ And finally, there's the sheer presumption of the Vatican in speaking directly to the Turkish public, as if it somehow represented the EU — of which it was not even a member. But this, of course, served to reinforce the idea that the EU was a Christian club and that Muslims didn't belong.