is “christianity” an abstraction?

But Christendom has abolished Christ; yet, on the other hand, it wants—to inherit him, his great name, to make use of the enormous consequences of his life. Indeed, Christendom is not far from wanting to appropriate them as its own merits and to delude us into thinking that Christendom is Christ.

SK (Institutions)

Is “christianity” an abstraction that, when used against the individual, is dehumanizing? When Nietzsche writes again Christianity, maybe he is right?

So, do I believe in Christianity or in Jesus?

Any thoughts?