From 1962 to 1967 he taught theology and canon law at the Major Seminary and the College of St. Vincent in Latrobe. Fr. Isaac also served as spiritual director in the Major Seminary and was pastor for a time of St. Cecilia Church, Whitney, Pennsylvania.

In January 1965 even before the close of the II Vatican Council a symposium of Jewish and Catholic theologians was held at St. Vincent’s Archabbey with Fr. Isaac as a behind the scenes organizer.  Torah and Gospel, Jewish and Catholic Theology in Dialogue edited by Philip Scharper (New York, Sheed and Ward, 1966) is the volume that contains the papers delivered in an atmosphere of warmth and wisdom at the three day event.