I think there is something more universal than those things found only in Christianity. This would be primarily the incentive for good social behaviour driven by a spiritual reward and some form of censure or punishment if you fail.
However the thing which got up the nostrils of the Roman authorities was the fact that chrestians (sic) that is "good" men or street preachers, in the first century began to teach that the saviour character of traditional (pagan) religious drama had magically come to life as a living man. This absurdity was beyond the pale for educated people but was the defining and mind boggling belief for those who later were called christians.
The NT is in part an apologia or defence for this doctrine, notably as is found in the Letter to the Hebrews. So perhaps the universal Christian belief is that Jesus or technically the Saviour character, became flesh. Consequent to this, as the story goes, he also died and was resurrected. . . justifying the equal absurdity of a universal but qualified resurrection for all.