Killing of animals before the advent of Lord Buddha was the most prominent feature of the society. People claimed that these were Vedic sacrifices. When the Vedas are not accepted through the authoritative disciplic succession, the casual readers of the Vedas are misled by the flowery language of that system of knowledge. In the Bhagavad-gītā a comment has been made on such foolish scholars (avipaścitaḥ). The foolish scholars of Vedic literature who do not care to receive the transcendental message through the transcendental realized sources of disciplic succession are sure to be bewildered. To them, the ritualistic ceremonies are considered to be all in all. They have no depth of knowledge. According to the Bhagavad-gītā (BG 15.15), vedaiś ca sarvair aham eva vedyaḥ: the whole system of the Vedas is to lead one gradually to the path of the Supreme Lord. The whole theme of Vedic literature is to know the Supreme Lord, the individual soul, the cosmic situation and the relation between all these items. When the relation is known, the relative function begins, and as a result of such a function the ultimate goal of life or going back to Godhead takes place in the easiest manner. Unfortunately, unauthorized scholars of the Vedas become captivated by the purificatory ceremonies only, and natural progress is thereby checked.
To such bewildered persons of atheistic propensity, Lord Buddha is the emblem of theism. He therefore first of all wanted to check the habit of animal-killing. The animal-killers are dangerous elements on the path going back to Godhead. There are two types of animal-killers. The soul is also sometimes called the "animal" or the living being. Therefore, both the slaughterer of animals and those who have lost their identity of soul are animal-killers.