Rabbi Shaar Yashuv HaKohen was the son of Rabbi David Cohen, "the Nazir," a disciple of Rav Kook. He fought in the defense of the Old City of Jerusalem in 1948, served as a rabbi in the IDF, and in the 1960s–70s was active in the public life of Jerusalem, including as deputy mayor. From 1975 he served for more than three decades as Chief Rabbi of Haifa, and was involved in interfaith dialogue on behalf of the Chief Rabbinate.
Some of these letters touch on public policy; they present the Rebbe's own position.
Torah in public life. The Rebbe encouraged him to use the opportunity of civil law reform in Eretz Yisrael to introduce Torah-based principles (IK 8447), and urged careful consideration of decisions affecting Jewish life in the Old City of Jerusalem, warning against letting other considerations harm Jewish unity (IK 9445).
Torah and scholarship. He taught that Torah works should be made as accessible as possible, with indexes and tables of contents (IK 7571), and asked for the published writings of his father, the Nazir (IK 9599). In a Pesach letter he wrote that spiritual growth requires recognizing one's personal limitations — one's own "Mitzrayim" — even within holiness (IK 7545).
Sources: Wikipedia ("She'ar Yashuv Cohen"); and the Rebbe's letters cited above.