His paper has nothing to do with a "return to Judaism", just a brief look that the Pharisees had a broad spectrum of followers. Some were against Christ, such as pre-conversion Paul, to secret followers such as Joseph of Arimathea.
I might add that due to the Jewish diaspora and missionary Pharisees (Matt 23:15), this set the stage for the early spread of Christianity by Paul during his missionary journeys. The focus of Pharisees was the synagogue and personal purity. Without these centers of Judaism scattered all over the Roman Empire, I imagine that Paul, and other disciples, would have found it harder to find a ready audience for the spread of Christianity.