[disclaimer - I'm Jewish and don't really know much about Christianity. If this is a simple/known question - please excuse me and point me in the right direction.]
Basically he suggests and brings support for the idea that Paul was really a "Jewish spy" sent to infiltrate the early Jewish Christian establishment and to steer it away from Rabbinic Judaism. The Rabbis at the time viewed Christianity as an significant threat in that the adherents looked and acted like the other Jews while holding some ideas that were/are viewed as heretical. By making Christianity more "non-Jewish," the followers would be distinct and separated from the Rabbinic Jews.
The implications of this are vast - it seems. Paul seems to have been responsible for some significant changes in the Christian dogma. If it could be shown that he really was a "Jewish spy", then it would seem we would have a major disinformation campaign that leave us unsure about what the founder of Christianity really was teaching.
Has anyone thought about what would Christianity look like if it rejected the teaching of Paul?