In the first three centuries of the common era, there was no single "Christian" view of who Jesus was. Instead, there was a Christological Spectrum. Depending on whether you were in the Jewish-Christian circles of the Jordan River or the Gnostic salons of Rome, your "Jesus" was a fundamentally different being.
For the Ebionites (the "poor ones"), Jesus was not a pre-existent divine being, but a human man—the child of Joseph and Mary—who was so devoted to the Mosaic Law that God "adopted" him as the Messiah at his baptism. This Adoptionist model allowed early followers to maintain their Jewish identity and their commitment to the Law, viewing Jesus not as a replacement for the Old Testament, but as its ultimate fulfillment.
The Political Conflict: By the end of the 2nd century, the Roman church declared Adoptionism a heresy. Why? Because a "human" Jesus is a Jesus who can be questioned. A "divine, eternal Logos" (as presented in the Gospel of John) is an absolute authority. Shifting the identity of Jesus from "adopted human" to "eternal God" was a crucial step in building an institutional hierarchy.
At the opposite end of the spectrum was Docetism (from the Greek dokeō, "to seem"). Docetists argued that the material world was so corrupt that a divine being could not possibly have a physical body. Therefore, Jesus only seemed to have a body and only seemed to suffer on the cross.
This was not just a theological quirk; it was a psychological necessity for the Gnostics. If the physical body is a prison, then the only "savior" is one who is entirely incorporeal. The "Word made Flesh" was, to them, a figurative metaphor for the descent of spirit into matter.
Perhaps the most dangerous figure to the emerging orthodoxy was Marcion of Sinope. Marcion didn't just disagree on the nature of Jesus; he proposed a Cosmic Divorce. He argued that the "cruel, despotic" God of the Old Testament was not the same as the "God of Love" revealed by Jesus.
Marcion's attempt to purge the "Jewish" elements from the faith—rejecting all but a redacted version of the Gospel of Luke—forced the Church to finally define its Canon. The "New Testament" as we know it today was created, in large part, as a defensive response to Marcion. The Church had to decide: are we a continuation of the Jewish story, or a brand new religion?
Modern historians like Bart Ehrman and Larry Hurtado debate whether this diversity was an "evolution" (slowly moving toward the Trinity) or a "Big Bang" (where high Christology existed from the start). Regardless of the timeline, the result was the same: the Nicene Creed was not a discovery of truth, but a political settlement that smoothed over these deep, regional divisions to create a unified Imperial front.