Rabbi A.Y. Kook is considered the spiritual and biological founder of the religious Zionist movement. Even at the date of the composition of these letters (the early twentieth century), when the secular Zionist movement was just beginning, and the Jewish state was still nearly 40 years away from its birth, we can see many of the conflicts and traumas that still afflict Israeli society reflected in his letters.
Kook was the first major Jewish religious authorities to embrace secular Zionism, but he did so on his own terms. Taking some notions from the Kabalah, he believed that even sinful behavior, such as the secular settlement activity of socialist Zionists, could be turned into merit. God would use those who He saw fit to settle the land. And eventually, they would all return to fold of normative Jewish practice.
So, Kook helped sow the seeds of the religious settlement project in the West Bank, and the general assault of secular rule of law in Israel. It is all here in these letters, although the tone and texture change depending upon who he is addressing. When he is writing friends and confidants, his tone is more strident. When addressing the non-religious, he uses a more conciliatory tone.
It seems Rabbi Kook was a deft politician, as well as a great spiritual leader.