He was born Feivel Gruberger in Brooklyn, New York, but later anglicised his name. Berg was ordained as a rabbi at the Torah Va Daath school before working as an insurance agent for 17 years, until 1970. He married Rivka Brandwein and had seven children. In the early Sixties, Berg travelled to Israel and met Rivka's uncle, Rabbi Yehuda Brandwein, then Dean of the Research Centre of Kabbalah.