Agudas Chabad is the umbrella organization of Chabad chassidim in Eretz Yisrael, and Tzeirei Agudas Chabad (Tzach) is its youth and outreach arm. These letters are addressed to their national executive committees, and span roughly 5712–5730 (1952–1970). See also Tzeirei Agudas Chabad, Jerusalem.
Spreading Chassidus, adapted to each place. The Rebbe taught that while spreading Chassidus remains central for Agudas Chabad groups, their efforts should be adapted to local needs (IK 2106), and that outreach must lead to practical growth by engaging local people directly (IK 2132). He urged Tzach's leaders to keep in regular contact and keep expanding their outreach (IK 2270), to tailor it to diverse audiences and maintain connection with people afterward (IK 7938), and to report regularly on their activities (IK 7962).
Orphans of war and terror. Several letters are the Rebbe's messages for the bar mitzvah celebrations Tzach organized for boys orphaned by war and terror: that a bar mitzvah marks spiritual responsibility, planned with sensitivity to each family (IK 9511), and that Torah, mitzvos — especially tefillin — and joy bring protection to the Jewish people (IK 9929). See also Mourning and loss – Widows and orphans.
Unity. For communal gatherings, the Rebbe urged unity among all participants, whatever their background (IK 10257).
Sources: the Rebbe's letters cited above.