Rav Tzvi Yehuda Kook on Vegetarianism: The Whole Unity of Reality
“…All the creations of the Holy One Blessed be He borrow from one another; the day borrows from the night and the night from the day”, and they do not judge one another (take each other to court) like people do, as it is said, “Day to day expresses speech…;” the moon borrows from the stars and the stars from the moon, and when the Holy One Blessed be He wants they do not appear, as it is said, “Who commands the sun to not shine; Who seals up the stars;”the light borrow from the sun and the sun from the light, as it is said, “Sun and moon stand at their dwelling…;”wisdom borrows from knowledge and knowledge borrows from wisdom, as it is said, “Say to wisdom you are my sister…”the heavens borrow from the earth and the earth from the heavens, as it is said, “God will open for you His bounteous store, the heavens, to provide rain for your land in season and to bless all your undertakings…;” kindness borrows from charity and charity from kindness, as it is said, “He who strives to do charity and kindness…;”the Torah borrows from the commandments and the commandments from the Torah, as it is said, “Keep my commandments and live, My Torah, as the apple of your eye;” the creations of the Holy One Blessed be He borrow from one another and make peace between one another without issues…” 
With this Midrash is expressed a whole outlook of unity of the overall cosmological reality, of all of existence, spiritual and material, “the team of all creations” in a wondrous and clear expression. And the ultimate peace, the whole connection of all being of the world, the inner and the actual harmony, in their collectivity, and their particularity, it is the true wholeness and the correct healthiness.
With this whole awareness of the unity of the cosmological reality in the full meaning, the question of eating animal meat can be answered in a way like this: there is in it, truthfully, in abstinence from eating animal meat, a foundation of misappropriation or superficiality, for only through the influence of our senses, or shall we say the crudeness of our concepts, would we distinguish between these creations that are called “living” and these that are called “not living”.” It goes without saying according to the theory of Platonic ideals that everything in the world has a type of soul, a drawing down of strength of spiritual essence (form), and as is known in the words of the Kabbalists about the subject of the soul of vegetable and mineral, but even according to the most simple awareness, that is really realistic, behold, like we do injustice in killing the living, in our nullifying with this procession of its energies and movements, so too we cause nullification and disturbance in such a way to the procession of the energy of the soil by our trampling on it along our way, of the air in every movement that is caused by every one of our breaths, and so too in every corner to which we turn and with every step that we take the injustice of our actions in our suppressing with a strong hand the strength of other creations for our private benefit. And in truth there is no real difference between eating the meat of animals and causing pain to animals in general and making use of them for any difficult labor or work, since even in this there is in the end lessening of its strength and its distress, it is just that there is a place for the superficiality of feeling to doubt this and not be depressed by force of our control are not absorbed and entered into our insides, our particular individual bodies. But is this a sufficient answer, since we have used up the energies and oppressed with our private strength, and we did this injustice- is it only in putting those energies into our individual bodies that the injustice of our actions is substantiated, and without this we can say to ourselves with clean hands, “Be at peace”?
In what is the foundation of our dividing line that separates between all creations, upon which all our powers and processes of our lives are based, that in every movement of the process of our lives we are permitted to push and to press them and to overturn the order of the process of their energies, and between those whose arrangement of their lives movements is in a way more prominent, ordered, and organized, that from them we are forbidden to take and to use them for our lives needs? And how much more so regarding vegetation, whose organization and vitality stands out even to our crude senses, and particularly in light of the decision of the latest science about signs of “the lives” of plants?
And if so, since this distinction between animal and plant is blurry and very weak and without real value in reality, and similarly awareness is expanding regarding the inanimate, regarding all creations, and constantly, really at every moment we annihilate and cause loss, break and oppress others for our own lives, (as is understood, as much as there a place for annihilation and loss etc.)- (then) there is not clear intellectual foundation for abstinence from eating animals specifically.
Indeed, only within the outlook of true and clear unity, pure and exalted, will that difficulty of spirit that makes this awareness burdensome for us be removed, that our lives, all its process and sustenance, is one chain of murders and loss of lives, whether they be animal, vegetable, or mineral. For only from a limited outlook on the particularity of actions in isolation would we be able to be remorseful about them and to judge them as evil actions, but within the outlook of whole unity we will not see ourselves as an isolated particular thing, and so too each and every creation of the world, not (just) living beings, not (just) vegetable and mineral, rather all them and all of us are actually one thing, like a single organic entity, all of whose parts are encompassed, unified, and connected together by an inner, origin-connected, natural bond, and all of them receive from one another and give to one another, then there is no place for these severities in the course of life, this one does not consume that one, rather all consumes all, and just like people provide for one another in the spiritual and material economy of life, so too is the case with all creations. So should man breath into himself the air of his breathing and pay the air with what he expels, which is needed for different creative purposes, or so the atmosphere pays man the different atmospheric fundamentals that it needs in exchange for what it receives from man. In this way man uses for his benefit in every way, with animals, and in exchange he supplies them their needs and watches over them, within the whole species, or the reverse, that with the price of supplying their needs and protecting them he will use them for his benefit “I will put grass in your field for your animal”  and afterwards “you will eat and be satisfied.”
And this reciprocal “business” calculation alone will not clarify for us the overall framework of the world’s order and thus quiet our spirit, and we will not be able to measure the extent of these laws according to the exact and focused receipt of give and take, which could indeed be focused and exact in the God of Knowledge’s weighing, but rather specifically the true whole outlook of unity, in which all creations are merged and stand within it in one synthesis, in which all of them are absorbed in the total existence of these “business” calculations, they also stand out from within the chain of cosmic and historical causation, according to sublime Providence, as overall calculations and whole ways of life and creation of the totality of existence.
But all this is from the perspective of objective contemplation alone, but from the perspective of subjective moral guidance certainly there is a place to distinguish between animals and eating them and other creations, since they express their distress and their oppression more obviously, which with our vital partnership with them and with the additional conspicuousness of the prominence of the difference between changes in their condition in front of us, it makes a more powerful and prominent impression on our psyche and on the paths of our morality. And this is the foundation for this fact that the main reason for the prohibition of causing pain to animals is in order to remove the characteristic of cruelty from our heart. And this fits with the statement, “Charity only pays according to the kindness it contains.” 
And after all this there is further room for the futuristic vision that in the future to come there is no eating or drinking at all, since in the time of the end of days together with the greatest and encompassing universal cosmological fulfillment, the individual characteristic specifically will also be elevated in wholeness, and there is no room then for one individual to receive bounty from his fellow, but rather for healthy and whole sustenance from drawing on the origin-connected, essential, individual bounty without association with other individual assistance, but only from amid the collective vital bounty, the benefit from the radiance of the Divine Presence, which will fill the perfect supply of all life and existence. “…for God shall be your light everlasting, your Lord shall be your glory.”
And the fact that in recent generations the non-importance or even the detriment of animal meat for man´s physical health is becoming clear and more agreed upon, it is possible that this also fits the process of becoming whole and the overall development of reality and man, whether from the perspective of the final, future, natural elevation, or whether from the perspective of moral development.
 Psalms 19:3
 Job 9:7
 Habakuk 3:11
 Proverbs 7:4
 Deuteronomy 28:12
 Proverbs 21:21
 Proverbs 7:2
 Exodus Rabbah 31:15
 Deuteronomy 11:15
 Sukkah 49b
 Isaiah 60:19