What was early Christianity like, including its relation to Judaism?

Early Christianity emerged from within Judaism, claiming to be its legitimate prophetic heir. The earliest apologists — Tertullian, Eusebius, Origen — defended the Christian movement by appealing to the antiquity of Jewish scripture: what Jesus fulfilled had been prophesied for centuries before the Roman Empire, placing Christianity on older and more credible ground than any pagan philosophy. Eusebius documents how the Old Testament prophets named Christ explicitly and predicted both Jewish opposition and the calling of the Gentiles, framing the Church's expansion as the fulfillment of Israel's hope. Josephus, writing as a non-Christian Jewish historian, independently corroborates the movement's Jewish origin, describing Jesus as a teacher who attracted both Jews and Gentiles. Clement of Rome interpreted "Christ" through Jewish anointing traditions — the same title given to Israel's kings and high priests — applying it to Jesus as the ultimately anointed one. The missions recounted in Acts — Paul and Barnabas preaching first in synagogues before extending to Gentiles — reveal the early Church's Jewish starting point and progressive expansion. Origen contrasted Christian monotheism with Greek mythology, positioning the Jewish-derived belief in one God against the fractured, immoral narratives of pagan religion. The relationship was not without tension: Origen and other Fathers engaged in sustained debate with Jewish interpretations of the Old Testament, arguing that Christian reading, not Jewish reading, represented the true fulfillment of the prophetic heritage both communities shared.