I did not find a reliable published biography of Yitzchak Damiel; this summary is drawn from the Rebbe's letters to him (about 5717–5720, 1957–1960), which show him to be an educator in Eretz Yisrael who corresponded with the Rebbe at length on questions of faith and education.
Faith and reason. Much of the correspondence is an ongoing conversation about faith. The Rebbe wrote that the standards people use every day — scientists included — to accept realities they cannot see apply equally to belief in the Creator (IK 6876); that while rational inquiry has its place, true conviction about G-d and Jewish values comes from within (IK 6898); and that true faith lies within every Jew, even when outwardly denied (IK 7403). He noted that intellectual answers alone do not satisfy the soul (IK 6959), and that understanding comes when questions are stated clearly and Chassidus is translated into meaningful practice (IK 7053).
Truth without compromise. The Rebbe wrote that real progress comes from recognizing the uncompromised truth, not from partial measures (IK 4729), and that Torah education must remain whole and uncompromising (IK 6309). He warned against adopting imprecise modern concepts such as "Israeli consciousness" in place of a clear commitment to authentic Jewish identity (IK 5766).
Education and influence. The Rebbe urged him never to withdraw from influencing his students, and to use every opportunity in Jewish education (IK 5471), advised him on where to teach and how to reach youth, and encouraged a Torah quiz initiative (IK 6539). He wrote that sincere efforts to bring Jews closer to G-d are always fruitful (IK 5600), and encouraged him to spread the teachings of the Baal Shem Tov and Chassidus (IK 7168, 7403).
Sources: the Rebbe's letters cited above.