(Srimati Lilavati Devi Dasi helping take the cows out to pasture at a farm in Suffolk, England)

Bhagavad-gita as it is, Chapter 14, Text 16 –

कर्मणः सुकृतस्याहुः सात्त्विकं निर्मलं फलम् ।
रजसस्तु फलं दुःखमज्ञानं तमसः फलम् ॥१६॥

karmaṇaḥ sukṛtasyāhuḥ
sāttvikaṁ nirmalaṁ phalam
rajasas tu phalaṁ duḥkham
ajñānaṁ tamasaḥ phalam

SYNONYMS
karmaṇaḥ—of work; sukṛtasya—in the mode of goodness; āhuḥ—said; sāttvikam—mode of goodness; nirmalam—purified; phalam—result; rajasaḥ—of the mode of passion; tu—but; phalam—result; duḥkham—misery; ajñānam—nonsense; tamasaḥ—of the mode of ignorance; phalam—result.

TRANSLATION
By acting in the mode of goodness, one becomes purified. Works done in the mode of passion result in distress, and actions performed in the mode of ignorance result in foolishness.

PURPORT

BG 14.16, Purport: A human being has no need to kill animals, because God has supplied so many nice things. If one indulges in meat-eating anyway, it is to be understood that he is acting in ignorance and is making his future very dark. Of all kinds of animal killing, the killing of cows is most vicious because the cow gives us all kinds of pleasure by supplying milk. Cow slaughter is an act of the grossest type of ignorance. In the Vedic literature (Ṛg Veda 9.46.4) the words gobhiḥ prīṇita-matsaram indicate that one who, being fully satisfied by milk, is desirous of killing the cow is in the grossest ignorance. There is also a prayer in the Vedic literature that states:

namo brahmaṇya-devāya
go-brāhmaṇa-hitāya ca
jagad-dhitāya kṛṣṇāya
govindāya namo namaḥ

“My Lord, You are the well-wisher of the cows and the brāhmaṇas, and You are the well-wisher of the entire human society and world.” (Viṣṇu Purāṇa 1.19.65)

The purport is that special mention is given in that prayer for the protection of the cows and the brāhmaṇas. Brāhmaṇas are the symbol of spiritual education, and cows are the symbol of the most valuable food; these two living creatures, the brāhmaṇas and the cows, must be given all protection—that is real advancement of civilization. In modern human society, spiritual knowledge is neglected, and cow killing is encouraged. It is to be understood, then, that human society is advancing in the wrong direction and is clearing the path to its own condemnation. A civilization which guides the citizens to become animals in their next lives is certainly not a human civilization. The present human civilization is, of course, grossly misled by the modes of passion and ignorance. It is a very dangerous age, and all nations should take care to provide the easiest process, Kṛṣṇa consciousness, to save humanity from the greatest danger.

from Bhagavad-gita As It Is by Srila A.C. Bhaktivedanta Swami Maharaja Prabhupada

Sri Go-puja, ki jaya!