“Christianity is the religion of Jesus.”
Jesus was a Jew. The religion of Jesus is Judaism.
Christianity is the religion of fourth-century Rome. Prior to the Council of Nicea in 325, “Christianity” consisted of hundreds of sects, all radically different, all claiming to be the “true religion of Jesus.” The Council of Nicea was convened precisely because all these sects were at each others’ throats. The Bible was created during this century, based upon a limited selection of Jewish texts, seven letters from Paul dating from around the year 50, and a collection of other written works (including the four Gospels) written around the year 100 and later.
The resulting Orthodox Catholic Christianity was a rework of the then-popular Roman worship of the Persian God Mithras, combined with a heavily-pruned Jewish variant of the dying-reborn god mystery religions of the ancient Mediterranean Pagan world. It bore little resemblance to Judaism in any form.
What most modern Americans recognize as “authentic Christianity” originated in the Protestant movement of the 16th century, as re-invented in the early 1900’s as “Fundamentalism,” based on a six-volume set of books (“The Fundamentals”) published between 1910 and 1915, then re-branded in the 1950’s as “Evangelicalism.”