One of my favourite seforim by Rav Kook is "The Moral Principles" (In Hebrew: Midot Harayah). It is published in english by Ben Zion Bokser in "Abraham Isaac Kook: The Lights of Pentience, Lights of Holiness, The Moral Principles, Essays, Letters, and Poems" as part of "The Classics of Western Spirituality" series.
Below is a the first excerpt from the chapter entitled “Love” from this sefer (Pg 135). More will be coming, so stay tuned.
2) The lovel of all creation comes first, then comes the lovel for all mankind, and the follows the love for the Jewish people, in which all other loves are included, sinice it is the destiny of the Jews to serve toward the perfection of all things. All these loves are to be expressed in practical action, by pursuing the welfare of those we are bidden to love, and to seek their advancement. But the highest of all loves is the love of G-d, which is love in its fullest maturing. This love is not intended for an derivative ends; when it fills the human heart, this itself spells man’s greatest happiness.
3) One cannot but love G-d, and this sweet and necessary love must engender as a practical consequence an active love for everything in which we perceive the light of G-d. One cannot but love the Torah and the commandments, which are so intimately linked to the goodness of G-d. One cannot but love equity and righteousness, the bening order that engenders good for all, which is firmly linked to the reality of existence, and in which the heart envisions excellence, that, becaue of its majesty and beauty, we designate as the will of G-d. The divine will is manifest in it, but it is greater than all this, and distinct from all this, and it nourishes the soul of every living being which delight beyond anything to which thought could reach. And it is impossible not to be filled with love for every creature, for the flow of light of G-d shines in everything, and everything discloses the pleasantness of the Lord. “The mercy of the Lord fills the earth” (Ps 33:5)