One of the most difficult leaders to characterize and paint into a sectarian box would be Rav Avraham Yitshak haKohen Kook. His writings are often as complex as they are prolific, and it would be a great disservice to approach his writings superficially. While it may be attractive to quote Rav Kook in a manner that is limited and self-serving, I would consider this an affront to his greatness as well as disingenuous. During my days at Machon Meir in Jerusalem I remember the political yardstick with which he was measured and it is not my intention to repeat such a callous approach to such an amazing figure.
As Benjamin Ish-Shalom writes in 'Rabbi Avraham Isaac Kook and Jewish Spirituality', Rav Kook expresses pluralistic views but should not imply that he was oblivious to making distinctions. In fact it should be noted that Rav Kook expressed the unique message as well as the ontological spiritual refinement of the Jewish people but felt such a message could be integrated within a pluralistic worldview; apparently without contradiction. Therefore I would stress the following within such a given context in order to give justice to his words.
'We must study all the sciences of the world, all the teachings of life, all the different cultures, and the religious and ethical doctrines of every nation, and with great broad-mindedness must understand how to purify them all.
Despite differences of opinion among religions and faiths, among races and climes, we should try to comprehend the different groups and peoples of the world to the best of our ability, to learn their nature and their characteristics so that we might know how to build human love upon practical foundations...and narrow-mindedness, which causes one to see all that is outside the bound of one's own nation, even if it be outside the bounds of the Jewish people, as nothing but ugliness and impurity is one of the worst kinds of darkness, which completely destroys the whole structure of spiritual good for whose light every noble soul yearns (OHK IV, p. 405)."
Further Suggested Reading:
Abraham Isaac Kook: The Lights of Penitence, The Moral Principles, Lights of Holiness, Essays, Letters, and Poems
The Essential Writings of Abraham Isaac Kook
Rav Avraham Itzhak Hacohen Kook: Between Rationalism and Mysticism
Rabbi Abraham Isaac Kook and Jewish Spirituality
Websites of Interest:
http://www.orot.com/
http://www.ravmosheweinberger.com/Department/Lecture_Series/Rav_Kook.html