How can Christians be so ignorant as to actually believe that their Christian religion is actually a fulfillment of Judaism?
The New Testament's theology is completely different from the Old Testament of the Hebrews. By reading the NT, one sees the introduction of certain themes that simply aren't found in Judaism, but that are very obviously influenced from Greek mystery rites. The entire concept of a suffering deity, of a deity whose suffering and death 'redeems' the world; the idea of followers mystically sharing in this deity's suffering, the strong emphasis on forgiveness of sins and salvation through belief, and of reaching a pleasant/'good' afterlife by performing proper rites and/or subscribing to a certain deity - these are all undeniably elements borrowed from Greek mystery religions and neo-Platonism! The Orphic rites, the Eleusinian rites, the Attic rites, the cults of Serapis and Dyonisus and Isis. These thematic elements are completely alien to Jewish theology, hence why the Jews themselves rejected (and still do) Christianity; there is no 'continuity' between the New or Old, save whatever convoluted excuses Christians use to attempt to reconcile the two.
Does Yahweh the war god ever give the impression of being a 'suffering deity'? Isn't it odd that the New Testament places undue emphasis on an afterlife, yet the Old Testament made no mention of it, such that the concept of an afterlife did not even develop until well into the Second Temple period? Isn't it strange that Jesus bore none of the attributes or signs that Yahweh himself promised the Jews the Messiah would have?
In essence, to put it in simplest terms - the New Testament is a Greek fanfiction to the Old Testament: it is not 'canon', and attempts to reconcile the two are just too problematic and self-defeating.