Grün finished his school years in 1964 with the A-level equivalent Abitur at the grammar school in Würzburg, Germany. In the same year he began as a novice at the nearby Benedictine Münsterschwarzach Abbey.
Grün finished his secondary education in 1964 with the A-level equivalent Abitur at the grammar school in Würzburg, Germany. In the same year, he commenced novice training at the nearby Benedictine Münsterschwarzach Abbey.