During the second temple period Jewish scribes and rabbis began to adopt binitarian theology. Alan Segal, a believing Jewish scholar, wrote a book about how this view developed. They were making observations about peculiarities in the Hebrew text that couldn't be explained without appealing to the idea that there were two persons in Israel's god, one invisible and one visible.
Amazon.com: Two Powers in Heaven: Early Rabbinic Reports about Christianity and Gnosticism (Library of Early Christology): 9781602585492: Segal, Alan F.: Books
www.amazon.com
I doubt that all 1st century Christians shared the same view on the nature of God. I'm sure many of them were unitarian. On the other hand, the NT writers did everything in their power to communicate Jesus' deity without conflating him with the Father God.
The reason I responded to your original post is because a number of unitarians will appeal to the shema to disprove trinitarianism. There are a number of ways one could go about defending unitarianism. But, the shema isn't really rich soil for debate on this topic. Even JWs apparently accept that the shema doesn't really interact with the trinity doctrine.
https://wol.jw.org/en/wol/d/r1/lp-e/2016445 (Paragraph 4)