Syncretism ... the worship of many deities while considering them truly to be manifestations of the One ... was the real religion of the Graeco-Roman world. Worshipping any one deity in no way excluded the worship of another. The more sniffy and traddy and 'Roman' emperors sometimes showed hostility to 'Oriental Cults' on the very natural traddy ground that these seedy greekish immigrant cults with their iffy foreign clergy and secret subversive ceremonies were displacing the good old Roman public sacrificial cults of Jupiter and Mavors, of Vulcan and Venus, of Dea Roma and the Genius of the Imperial House. But persecution, real persecution, was reserved for those who worshipped Iesous ho Chrestos. Because Christianity was regarded, and very truly, not as just another name and cult for worshipping the One; it was recognised as a denial of all other gods and goddesses. That is why Christians were held to be, were loathed as being, Atheists.
At Acts 4:12, S Peter says "There is no other Name given among men under heaven in which it is necessary (dei) for us to be saved." That is the essential truth which distinguishes Christianity from Isiacism, Mithraism, and the rest. I know no better way of situating S Peter's statement in its original cultural and religious context than to quote, again, the Metamorphoses of Apuleius, Book XI.
"The Phrygians call me the Mother of the Gods; the Athenians, Kekropian Athene; the Cypriots, Paphian Aphrodite; the Cretans, Dictynnian Artemis; the Sicilians, Infernal Persephone; the Eleusinians, Demeter ..." etc. etc..
The Christian God is not known by many peoples under many names and worshipped through many cults; He is known universally by One People under One Name and worshipped at One Altar.
That is why S Paul insists that the Gods of the heathen are demons and insists, further, that worshipping them, and worshipping the Father and His Incarnate Word, are mutually exclusive (I Corinthians 10). Some of his converts undoubtedly had been, and were prepared to continue to be, syncretists.
No. We do not, as well-meaning people sometimes say, "all worship the same God really".
This is the Faith our martyrs died for.
That is what makes it different.
I once received a hostile comment from somebody who criticised me for referring to Cardinal Ravasi without mentioning his Eminence's name. So I rectified that detail. He then criticised me for writing about Ravasi without actually knowing what was in his mind. Actually, that was why I had refrained from mentioning his name. I did not really want to do business in terms of personal denunciations. And, finally, my correspondent went on to exculpate Ravasi by surmising that he thought that "paganism's reverence for the earth and its fertility is a valuable religious impulse that needs to be respected, purified, and inculturated into Christianity". So here we had the insidious old temptation to revert to the Fertility cults of Palestinian religion which the Prophets denounced, still exercising its ancient and seductive charms!
Perhaps, indeed, I grant, there are things we do not know about the scene which was recorded by the videoclip on the Internet. Perhaps there are ways in which a new light could be cast upon Ravasi's actions. I hope so. I am not in a place to pass judgement upon another, nor do I do so. But cardinals, above all, honoured as they are with the bright colour of martyrdom, the colour of the blood which twenty Coptic peasants poured out a couple of years ago upon the shore of the Mediterranean, have a duty not to give scandal. And to appear to take part in what has been widely publicised as a ceremony in honour of a deity whose name is not Jesus, is, prima facie, to behave scandalously. If this is not what Ravasi did, then I am profoundly relieved. But it is clear that he still has a duty to repair an apparent scandal. If some other person has grossly misrepresented actions which were every way proper, then that person has a scandal to repair, and, additionally, owes his Eminence an apology. Since Ravasi is a cardinal presbyter of the Roman Church, I think his bishop also has some responsibilities in this matter.
I can offer a Patrimonial discussion of Syncretism; C S Lewis dedicated an entire volume to it: The Last Battle.