These letters (roughly 1962–1970) are addressed to the congregation Kehillas Adas Yeshurun, mostly messages for its annual events in support of Torah education, including the Tomchei Temimim yeshivos. I did not verify the congregation's location from published sources.
Children and continuity. The Rebbe wrote that our greatest achievement is ensuring that our spiritual values are inherited by our children (IK 8691), and that Jewish identity endures through strong Torah education, proudly keeping our names and traditions (IK 9806).
Supporting Torah education. Supporting Torah institutions with money, effort or time elevates the giver's material life (IK 9617); supporting Tomchei Temimim brings both spiritual growth for Jewish youth and blessing (IK 10011); and supporting Torah education is an unparalleled investment whose returns multiply (IK 10258).
Light against darkness. Chanukah calls for spreading light through more Torah study and support for education (IK 8274), and for defending inner holiness, not only outward observance (IK 8921); increasing light through Torah and mitzvos dispels modern darkness (IK 9419). Even mundane daily activities should be infused with a higher purpose (IK 10584).
Sources: the Rebbe's letters cited above.