If we really want to cultivate the human spirit in society we must have first-class intelligent men to guide the society, and to develop the finer tissues of our brains we must assimilate vitamin values from milk. Devotees worship Lord Sri Krsna by addressing Him as the well-wisher of the brahmanas and the cows. The most intelligent class of men, who have perfectly attained knowledge in spiritual values, are called the brahmanas. No society can improve in transcendental knowledge without the guidance of such first-class men, and no brain can assimilate the subtle form of knowledge without fine brain tissues. For such important brain tissues we require a sufficient quantity of milk and milk preparations. Ultimately, we need to protect the cow to derive the highest benefit from this important animal. The protection of cows, therefore, is not merely a religious sentiment but a means to secure the highest benefit for human society.

Srila Prabhupada; Light of the Bhagavata 27, Purport