Complex sentence: Recently, scholars have begun to question this historical picture, arguing that during Second Temple period many competing Jewish sects existed in Judea and that what became Rabbinic Judaism and Proto-orthodox Christianity were but two of these.
Split into simpler sentences: Recently, scholars have begun to question this historical picture, arguing that during Second Temple period many competing Jewish sects existed in Judea. The sects which eventually became Rabbinic Judaism and Proto-orthodox Christianity were but two of these.