Trinitarian christians most certainly reject Judaism. You seem to assume and equate early Jewish "belief" to that of today's trinitarians.
Trinitarianism has nothing to do with any alleged rejection of Judaism. Jews recognize that God manifests Himself by His Wisdom, Word and Spirit (Trinitarian manifestation of God). Christianity redefined Judaism within Judaism. St. Paul certainly considered himself a Jew. Christianity was rejected by Judaism, not the other way around.