Śrīla Bhakti Siddhānta Saraswatī Ṭhākur explains the necessity of eating only to serve the Lord.
Translated from a Bengali quotation
published in Śrī Gauḍīya Darśan,
Volume 1, Issue 10,
on Thursday, 10 May 1956.
The scriptures say (Manu-smṛti: 1.49), “Antaḥ saṁjñā bhavanty ete sukha-duḥkha-samanvitāḥ [Plants have internal consciousness and experience pleasure and pain]”. Trees, vines, grass, shrubs, herbs, and so on are all souls endowed with consciousness. Therefore, even one who considers oneself a vegetarian in fact commits violence against other souls. Vaiṣṇavas are not non-vegetarians or vegetarians. They accept prasādam offered to the Lord that is approved by the pure scriptures and maintain their life for the purpose of serving the Lord. Fish, meat, and other unholy things are never fit to be offered to the Lord; they are the food of people in the mode of ignorance. Even green leaves, vegetables, and other vegetarian foods, if they are not taken as the prasādam of the Lord, and even when they are, if they are thought to be material foods and seen only for the purpose of one’s own taste, then by eating them, violence against other souls is perpetrated.