James L. Kugel and Rowan A. Greer, Early Biblical Interpretation, ed. Wayne A. Meeks (Philadelphia: Westminster, 1986) 122.
The legislation of the fourth and fifth centuries protected the Jews but prohibited them from any real participation in the life of the empire. At the same time, it was the "concurrence" of Christianity and Judaism that forced rabbinic Judaism to abandon many earlier Jewish notions and to take its stand on the one God of Israel and his Torah. For example, Jewish speculation about Wisdom could go so far as to treat Wisdom as a symbolic figure representing aspects of God or to identify Wisdom with the Torah. But when Christians identified Christ with Wisdom, monotheism seemed compromised; and the Jews were obliged to abandon ideas that might well imply a sort of polytheism.
A friend of mine at Harvard once told me that Judaism was not strictly monotheistic prior to its encounter with Christianity. I'm not sure what he had in mind, but we do see ideas in Judaism that appear to compromise a strict monotheism. Philo in the first century C.E. discusses the Logos, a representative of God whom Philo goes so far as to call a "second God" (Questions and Answers on Genesis 2:62). And targumim (many of which were contemporary with Christianity) refer to God's representative as the "memra," or "Word." Whenever the Hebrew Bible says "God" does something, the Aramaic translation generally states that the "memra" did it. The idea was probably that God was too transcendent to interact with human beings, so God had his Logos or memra act on his behalf. This would include the creation of the universe.
At some point, the rabbis criticized the view that God had help when he created the heavens and the earth. The Tosefta Sanhedrin 8:7, which dates to around the third century C.E., denies that God had a partner in his act of creation. Rabbinic literature speaks often against the "two powers" doctrine, and there are different perspectives that it could have had in mind. Prominent strands of Greek philosophy held that there was a transcendent God as well as a Demiurge, a being who fashioned matter into an orderly cosmos. The Gnostics thought that the Demiurge was a malevolent sub-deity who became the God of the Old Testament, and they exploited the "Demiurge" idea to support their claim that matter was evil, since it was made by an evil being. Add to that Philo's view that the Logos was the creator, and the claim by many Christians that the Word who became Jesus Christ made the heavens and the earth. For some reason, the rabbis decided to become stricter in terms of monotheism, holding that one God and one God alone was the creator.
Michael Brown, in Answering Jewish Objections to Jesus, Volume II, tries to do something with the concepts of the Logos and the memra, though I'd probably have to read him more closely to understand what. His goal is often to demonstrate that Christian ideas (e.g., a plural God, the substitutionary atonement, etc.) are actually consistent with Jewish sources. Maybe he's trying to make that claim in his treatment of the Logos and the memra: to show that the Christian idea of a "second God" also existed in Jewish writings, so Jews today wouldn't betray their Jewish heritage were they to believe that Christ is divine. Brown's not overly dogmatic about Philo, however, for he acknowledges the possibility that "Philo's description of the logos may have been philosophical, speaking of divine attributes in highly personified terms" (22).
Did Philo see the Logos as "God" in the same way that Christians today view Jesus as divine? Most Christians believe that Jesus is co-eternal with the Father, meaning he has always existed and was never created at a specific point in time. They hold fast to the fourth century Nicene doctrine that God the Son was "begotten, not made," meaning he always extended from God the Father, while being of one substance with him.
Philo, however, states that the Logos was "neither...uncreate as God, nor yet created as you, but being in the midst of these two extremities" (Who Is the Heir of Divine Things 206; Yonge's translation). Philo may mean here that the Logos had an origin, yet he wasn't like the rest of us created blokes (e.g., temporal, transient, etc.). I don't know.
I vaguely recall reading in Heinrich Graetz's History of the Jews that Philo saw the Logos as an angel, and Graetz (a nineteenth century Jewish historian) may have been trying to preserve Philo's reputation as a monotheist, while holding off Christian arguments of "You see, even Jews had an idea that there could be another God-person. So why don't you all believe in Jesus?" And yet, Philo does call the Logos a "second God," even though he may not have had in mind the same thing Christians later did when they called Jesus "God the Son"--eternally pre-existent, begotten not made, etc.
One thing I've come to appreciate from James McGrath's posts is that the term "god" in the ancient world could be pretty fluid in meaning. So when John 1 says that the Word was God, does that necessarily mean the same thing that Nicene Christianity later had in mind? I like this passage from McGrath's lecture, Are Christians Monotheists? The Answer of St. John’s Gospel:
...Philo and John both speak of the Word as mediator of creation, as one who is part of the reality of God and yet distinct from and subordinate to God. Both refer to the Word as 'God', and yet both emphasize that the Word is subordinate or inferior to the one true God who is above all. Philo makes this point by referring to the Word as a 'second God', while John makes this point by portraying Jesus as calling the Father "the only true God" in John 17:3. For both, then, the Word is an expression of the reality of God himself, and yet distinct from and subordinate to God, in a way that can only be described as paradoxical. Yet in spite of this paradox, it is clear that if Philo fits our portrait of what a first-century Jewish monotheist looks like, then so also does John: both held that there was one God above all who was uniquely worthy of worship, who created all things through his Word. There is unambiguous evidence that Philo understood himself to be a monotheist: he wrote the following words: "Let us, then, engrave deep in our hearts this as the first and most sacred of commandments, to acknowledge and honour one God who is above all, and let the idea that gods are many never reach the ears of the man whose rule of life is to seek for truth in purity and goodness" (Decal. I. 65). This comes from the pen of the same Philo who speaks of the Word as a 'second God'! It thus becomes clear that both Philo and John - and many other Jews of their time - felt that belief in one God who is above all is compatible with belief in a second figure who reveals and represents God. John's belief was different from Philo's in that he identified this Word with Jesus, but on the question of the oneness of God, it seems that they would have both agreed.
This is probably the best defense of Christian unitarianism that I've encountered. Most try to explain away the Word being God, but McGrath here acknowledges that John sees the Word who became Jesus Christ as God. It's just that "God" could refer to a sub-deity who created the universe, not necessarily an eternal person in the Godhead. In this model, God the Father is technically the "only true God," yet the Logos is also "God," in some sense.
At the same time, I suppose advocates of Nicene orthodoxy can appeal to John 1:3: "All things were made by him; and without him was not any thing made that was made" (KJV). If something came to be, then the Word made it. Doesn't that imply that the Word himself did not come to be, but always existed? I'm sure Unitarians and Trinitarians debate about how strict and literal we should be with that verse!
For good links on these issues (e.g., Logos, memra, two powers, monotheism), see Nick Norelli's post, Was Paul a Monotheist?