Dr. Zvi Harkavy belonged to the distinguished scholarly families of Strashun and Harkavy of Lithuania. He was an important figure in the Mizrachi movement in Israel, edited many scholarly volumes and wrote more than 150 articles. Among his works, he co-edited (with Yaakov Goldbourt) Sefer Yekaterinoslav-Dnepropetrovsk (Jerusalem, 1972), the memorial book of the city where the Rebbe grew up and where the Rebbe's father, Rabbi Levi Yitzchak Schneerson, served as rabbi.
Scholarship and publishing. Much of the correspondence is about scholarly and publishing matters. The Rebbe thanked Dr. Harkavy for the scholarly works he sent and encouraged him to keep sharing Torah insights (IK 9474). He wrote about the value of chassidic gatherings and the responsibility involved in publishing (IK 2078), and — while declining to take sides in printing disputes — urged that Chassidus be made accessible to all, especially today (IK 8779, 8824). A letter now sold at auction shows the Rebbe explaining that, following the practice of the Previous Rebbe, he does not allow his writings to appear in Festschrift volumes.
Israeli ships on Shabbos. Dr. Harkavy corresponded with the Rebbe on the controversy over Israeli ships sailing on Shabbos. The Rebbe maintained firmly that traveling on them on Shabbos is forbidden, whatever technical arrangements are proposed, and that Torah must guide every aspect of life (IK 5633, 6618).
Chassidus and Jewish unity. The Rebbe explained to him what it means to be a chassid — selflessly caring for others beyond personal calculation (IK 2136) — and stressed Jewish unity despite differences of opinion (IK 8719). On Rosh Hashanah and the new year, see IK 9233.
Note: one letter in this topic, to "Dr. Hercberg" (IK 7391), may be addressed to a different person.
Sources: Kestenbaum & Company auction catalogue (letter of the Rebbe to Zvi Harkavy); Chabad.org ("Birth and Upbringing," citing Sefer Yekaterinoslav-Dnepropetrovsk); and the Rebbe's letters cited above.