The just man knows the soul of his beast, but the heart of the wicked is merciless.
The author of Proverbs stresses an important ethical lesson: a humane person considers the needs of his animals and acts kindly towards them. The world of Creation is full of sentient beings, which also experience many of the joys and blessings that people commonly enjoy: like humankind, these creatures also experience pain. Suffering is a common language that links humanity with other species of animal life.
Therefore, Jewish ethics take sharp issue with French philosopher Rene Descartes (ca. 1596–1650), who compares animals to machines that service people, stating that their suffering “means nothing more than the creaking of a wheel.” In physiological terms, according to Descartes, what human beings and animals share is that their bodies function by the laws of mechanics. One might respond: How then do human beings differ from animals? Descartes argues that the Creator endows human beings with a divine soul and a moral conscience—qualities that are lacking in animals.
In addition, unlike animals, human beings possess the ability to conceptualize and verbalize ideas. Most importantly, only human beings are capable of conscious and rational thought since they are uniquely endowed with the ability to be self-reflective. Only a human being is capable of exclaiming, “Cogito ergo sum.”
Philo of Alexandria explains that the Mosaic proscription prohibiting the boiling of a kid in its mother’s milk aims to teach Israel that mercy and self-restraint should govern people’s relations with animals no less than with each other. According to biblical law, a person may not satisfy his or her appetite disregarding the feelings of animals, especially where mothers and their young are concerned. A worshipper in ancient times, for example, is barred from sacrificing a newborn animal until it is at least eight days old (Exod. 22:28–29; Lev 22:27).
He writes, “Nothing could be more brutal,” writes Philo, “than to add to the mother’s birth pangs the pain of being separated from her young immediately after giving birth, for it is at this time that her maternal instincts are strongest.” In other respects, too, the Law calls for self-restraint. Thus, it would be an act of unnatural excess, Philo argues, to cook a young animal in the very substance with which nature intended it to be sustained. In a similar vein, the Law prohibits one from sacrificing an animal together with its young (Lev 22:28), since this would again involve an unnatural combination of that which gives life and that which receives it.
 R. Yehuda HaHasid of Regensburg notes: “The cruel person is he who gives his animal a great amount of straw to eat and on the morrow requires that it climb up high mountains. Should the animal, however, be unable to run quickly enough in accordance with its master’s desires, his master beats it mercilessly. Mercy and kindness have in this instance evolved into cruelty.” Quoted from Noah Cohen’s Tsa’ar Ba’ale Hayim — The Prevention of Cruelty to Animals (New York: Feldheim Publishers, 1959), 45–46.
 Discourse on the Method of Rightly Conducting the Reason, and Seeking the Truth in the Sciences, ch. 5, 92-93.
 Philo, Virtues 125-44.
 Philo’s explanation is later found in the commentaries of Ibn Ezra, Rashbam, Ramban, Bechor Shor, Abarbanel, Aharon Eliyahu and S. Luzzato. On the other hand, Bechor Shor supposes that it also refers to the cooking of the kid, before it has been weaned from its mother’s milk.