Rav Kook is the greatest Jewish thinker in the last 200 years. He is the one who most understands the spiritual crisis of the modern Jew. The book "Orot" (Lights) is one of his most important works. Here he explains his views on the role of "Am Israel" (the Jewish people) in bringing G-d's message to the world. He explains the importance of the return of the Jewish people to its historical, Biblically-mandated homeland in Eretz Israel (The Land of Israel). Unlike some other religious Zionist thinkers who generally look at Zionism's role as simply facilitating the "ingathering of the exiles", Rav Kook shows in this book that the inherent holiness of the land mandates that the Jewish people settle and develop as much of it as possible, and not simply satisfy themselves with a small community residing on a small fraction of its divinely-mandated boundaries. A strong Jewish life, in all its manifestations, spiritual, economic, military, scientific in the whole Land of Israel will benefit not just the Jewish people, but its Arab neighbors and all of mankind as well.
Rav Kook's writings are generally difficult for the novice reader, even someone who is fluent in Hebrew. Rav Samson's translation into English and his cogent explanations of the text makes part of this classic text available to the wider Jewish world, just when it needs it the most, as the Jewish world confronts doubts among parts of the Jewish people (both religious and non-religious) over the Jewish people's very rights to Eretz Israel in addition to a violent onslaught by non-Jews against the Jewish nation. I also recommend Rav Samson's continuation of the translation of "Orot" called "War and Peace" where he deals with vast historical trends and wars that impact the Jewish people and its redemption.