The full divinity of Jesus (the Trinity) does not come until much later on.
In my opinion, what the earliest Jewish Christians believed (and I could cite the specialist literature here) is the following:
(1) during most of his lifetime Jesus was a human prophet, born of ordinary parents (no virgin birth, no incarnation, and no divinity) prophesying the imminent arrival of the “kingdom of god”: the end times where Israel would get its Messiah and be freed from the bloody and cruel tyranny of Rome. Jesus was thought to be a miracle working prophet, just like Old Testament prophetic figures who possessed the holy spirit (see M. D. Goulder, “A Poor Man’s Christology,” New Testament Studies 45 : 332-348).We also have to remember that Messianic movements could develop in extraordinary ways, even in modern times: we need only think of Sabbatai Zevi in the 1600s.
(2) by the time of the Jerusalem passover events, possibly Jesus either (a) now thought of himself as the Messiah or (b) many of his followers and ordinary people in Jerusalem thought he was Messiah (whether Jesus explicitly denied this or “tacitly” accepted it and allowed it, who knows?); he was killed by the Romans as a Messianic pretender, for disturbing the peace and for treason (what the Romans called the crime of maiestas).
(3) the movement collapsed after Jesus’s death and the disciples fled back to Galilee (this appears to be the earliest tradition implied in Mark and Matthew). There they had visions of Jesus and think he has been resurrected. Later they appear in Jerusalem proclaiming this.
(4) Jesus is now proclaimed Messiah - Israel’s king - and resurrected “son of god” (that is, as the Israelite kings were “sons of god” - but not in a divine sense). Jesus is now like the exalted prophet Elijah (the OT imagines Elijah being exalted to heaven to become a heavenly being), except he died and was raised to heaven.
(5) Jesus is now a heavenly king and Messiah, who will return soon, an exalted figure and god’s chief agent.
The early Christians do call Jesus “lord” and no doubt this title began as a merely earthly title for teacher or “rabbi.” But now when used of the exalted Jesus it starts to have a quasi-blasphemous ring to it to non-Christian Jewish contemporaries, for “Lord” is also the proper title for god.
Nevertheless, Jesus is not, strictly speaking, divine for early Jewish Christians: there is only one god, and Jesus is not in the same category.
(6) I suspect that the apostle Paul creates the notion of Jesus’s pre-existence: certainly he teaches this (he needs it for his new gospel of freedom from the Mosaic law), and probably Paul assimilated Jesus to personified attributes of god like “wisdom” or the “logos” or a first-born, angelic chief agent, ideas actually common in 1st century Hellenistic and Palestinian Judaism.
See the excellent book of Larry Hurtado, One God, One Lord, which shows how second temple Judaism had exalted heavenly figures like personified divine attributes (wisdom, the logos), exalted patriarchs, and chief agents/angels.
Paul invents the notion of the incarnation (though not the virgin birth) but makes it clear that Jesus, as a pre-existent heavenly being, does not want equality with god (full divinity) in Philippians 2.6–8:… Χριστῷ Ἰησοῦ, ὃς ἐν μορφῇ θεοῦ ὑπάρχων οὐχ ἁρπαγμὸν ἡγήσατο τὸ εἶναι ἴσα θεῷ, ἀλλὰ ἑαυτὸν ἐκένωσεν μορφὴν δούλου λαβών, ἐν ὁμοιώματι ἀνθρώπων γενόμενος• καὶ σχήματι εὑρεθεὶς ὡς ἄνθρωπος ἐταπείνωσεν ἑαυτὸν γενόμενος ὑπήκοος μέχρι θανάτου, θανάτου δὲ σταυροῦ.Nevertheless, by this stage Paul’s Jesus is looking quasi-divine.
“…. Christ Jesus
who, being in the form of God did not deem it a prize to be equal with God,
but he emptied himself, taking the form of a slave
born/becoming in the form of men,
and having appeared (or having been found) in shape as a man
he humbled himself, becoming obedient until death
and death on a cross.” (Phil 2.6–8).
(7) by the time of the gospel of Matthew (c. 80 AD), a liberal Jewish Christian invents the virgin birth from a garbled reading of Isaiah.
(8) By the time of the gospel of John c. 90-100 AD, you have Jesus as a pre-existent, first-born god: “in the beginning was the Word (logos), and the Word was with god, and the Word was god” (John 1:1). This is a development of Philippians 2.6–8 making explicit what Paul seems to deny (“Christ Jesus ... did not deem it a prize to be equal with God”).
(9) A few centuries later we have the Trinity, and so on. Christianity has become a religion for Greeks and Romans: Jesus is just another saviour god like Mithras, except his incarnation and death occurred in the recent past.
Jewish Christianity survives and seems to be reject Paul’s quasi-divine view of Jesus: Origen (Contra Celsum 5.65.5) tells us that “there are some sects who do not accept the epistles of the apostle Paul, such as the two kinds of Ebionites [= Jewish Christians].” And Eusebius tells us that both sects of Ebionites rejected Jesus’s pre-existence.
There is evidence that he actually signed letters with what was to many members of the Jewish community the most blasphemous phrase:
“the Lord, your God, Sabbatai Zevi” (Heinrich Graetz and Bella Lowy, History of the Jews, Vol. V, p. 143).Yet Sabbatai Zevi still attracted a vast Jewish following during his lifetime.
And this was not after he died and his disciples claimed he had been resurrected, but when he lived!