Indeed, G-d is kind and merciful, and His mercies are over all His works. Man is duty-bound to emulate Him, and Israel, His nation, are commanded to wear the mantle of mercy and show mercy to all His works. Our sages therefore declared (Shabbat 128b), “The prohibition against causing living creatures pain is Torah-based,” and (Gittin 62a), “A man is forbidden to eat until he feeds his animals. First it says, ‘I will put grass in your fields for you cattle’ (Duet. 11:15), and only then, “You shall eat and be satisfied’ (Ibid.).”
Moreover, G-d tests man’s leadership potential according to the extant of his mercy for G-d’s creatures. ( Shemot Rabbah 2:2) teaches:
His eyes behold, His eyelids test, the children of men (Ps. 11:4): Whom does He test? The righteous, as it says, “The L-rd tests the righteous” (Ibid., v.5). How does He test them? Through shepherding.
He tested David this way and found him to be a fine shepherd: “He took him from the sheepfolds” (Ibid., 78:70). What are “the sheepfolds [machla’ot]”? It is like “The rain was held back [vayikalei]” (Gen. 8:2). He would restrain the older animals for the sake of the younger ones. First he would let out the youngest to graze so they would get the soft grass. Then he would let out the aged animals so they would get the medium grass. Finally he would let out the young adults to graze on the hard grass.
G-d said, “let one who knows how to herd sheep according to their individual strength be the shepherd to My people.” As it says (Ps. 78:71), “From following the ewes He brought him to be shepherd over Jacob His people.”
G-d tested Moses, as well, precisely through shepherding. Our sages say that when Moses was tending Jethro’s Chasit, where it found a pool of water and stopped to drink. When Moses caught up with it, he said, “I did not know that you ran away because you were thirsty. You are tired!” and “he picked it up and carried it back on his shoulder. G-d said, “As I live! Since you have the compassion to tend sheep this way, you shall tend My flock, Israel.”
This is how far a Jew’s mercy must extend—to the little lamb, the flock of sheep, so great is the mitzvah of showing mercy. Yet it must always be in the right time and place in accordance with the dictates of Halacha, Jewish law, and the Divine conception of mercy. Let us never forget the mitzvah of not showing mercy where forbidden to do so.
Our sages said (Shabbat 151b), “Whoever shows mercy to his fellow man shall be shown mercy by G-d, and whoever does not show mercy to his fellow man shall not be shown mercy by G-d.” Let the reader understand that our sages learned this principle from a verse quoted immediately following the command to burn and destroy the ir ha-nidachat, the apostate city (Deut. 13:18): “God will make you merciful and have mercy on you.”
Precisely this indicates a Divine decree. It shows that the definition of “mercy” and love of Israel” are what G-d defines them to be, and not the mercy of fools enslaved to alien culture.
Kindness and mercy – in the right time and place – is the obligation of every Jew. It is a means of suppressing one’s passions and becoming less selfish, thereby exalting oneself almost to the level of the ministering angels, and perhaps higher. Hence, from the general theme of kindness and mercy emerge countless mitzvoth and ideas which have always guided the Jew in his daily life. (Or HaRa’ayon, Rabbi Meir Kahane p.178)