That was the whole point. Christianity was intended to be a break from Judaism. God took an anger management class and came back with his temper under control. He freed the Jews from the Covenant, the breaking of which had been his excuse for treating them like cockroaches.
No more "vengeance is mine," instead he sent down the First Hippie to teach his people a new culture of love and peace. No more "an eye for an eye," but instead "turn the other cheek." No more "Chosen People," anybody who wants to be one of God's children can be one, without having to be born into it. Instead of being an exclusive religion like Judaism, Christianity is an evangelical religion that is downright aggressive about making converts.
So naturally there was a break with all of the old ways. No more gospels written in a dead language (Hebrew), that children had to study in order to understand; the New Testament was propagated in the vernacular language of each people. All of the old rituals were replaced with new ones, including the ways of praying. Even much of the actual religion written in the Torah was downplayed as the New Testament replaced it as the primary source of understanding.
Christianity didn't really begin to develop, and the New Testament was not written down, until some time after Jesus's death. So a discontinuity between the religious practices during his lifetime and the practices codified by the priests who came later is understandable. They wanted a clean break from Judaism.
What you understand to be 'Christianity' was never intended to be a break from Judaism. Judaism and all its trappings are a 'shadow' cast by Christ, The Redeemer. The shadow is separate and distinct from that which casts the shadow… You don’t find in the shadow any substance or connection to that which casts the shadow.
However, Jesus the God-Man, does share a connection with ALL of humanity by virtue of His Incarnation...and Jesus is humanity’s ONLY Priest, descended from the tribe of Judah (by the Law, all Hebrew priests come only from the tribe of Levi ) according to a Promise/Covenant made by God to the
gentile, Abraham--430 yrs. before the institution of Judaism. The point of Judaism (the shadow) was to lead the Hebrews (and anyone who cared to join them) back to the Reality casting the shadow. This was done through continual, vivid, reminders of their inability and unrighteousness i.e. the sacrificial system and the stringent demands of the Law itself— this was a gracious way of giving man a chance to experience ON HIS OWN what he had sought in Eden: knowledge of right and wrong with the option of choosing right rather than wrong…the chance to be like God Himself...by this God unmistakably demonstrates the utter folly of desiring such things apart from Him, and accordingly they proved themselves utter failures in playing God…seeking to cover/hide their failure they began sewing together fig leaves of religiousity, rituals, and rules beyond that given by God originally, thus compounding their guilt.
When the God-Man walked among them, He removed their fig leaves an exposed their shame, underscoring their need not for resolutions to try harder but for re-connection to Him as their Source of ability and Identity (the way God intended Man to live all along)... Sadly, most wanted nothing to do with Him.
Yet--ironically/paradoxically-- when humanity does reconnect with God in Christ, humanity indeed receives all they sought for in Eden…i.e. to become like God Himself; to possess the knowledge of good and evil; to possess the Power and Ability to choose good rather than evil…all that and more is given humanity in Christ.
Redemption--not 'Christianity' has been the plan and purpose of God from the beginning and so He hasn’t 'changed' at all. He's taken great pains to clearly demonstrate our need for Him as the Source of Life, and, His Love for us as those who share a connection to Him enjoyed by no other creature.
