Translated by Ralph Anzarouth and an anonymous friend
Kindness means worrying and feeling sympathy for the misfortunes of others. This trait can take two forms: the one is called spiritual kindness and the other is called material kindness.
Examples of spiritual kindness are as follows: forgiving offensive acts; reproving one's fellow man who is going astray; providing wisdom to the simpletons; giving advice to the uncertain people; comforting the mourners; visiting the sick and praying for them and for all those who suffer adversity both for one’s friends and enemies as well as for the living and for the dead.
Examples of material kindness are as follows: providing food to the hungry, drink to the thirsty and clothing to those who need it; extending hospitality; redeeming captives; burying the dead.
The performance of these acts [of kindness] should be primarily out of love for Hashem and not because of any worldly motives neither for honor nor for glory. In this connection King Solomon said (Proverbs 21, 21): "He who pursues acts of charity and kindness will find life, justice and honor".
This trait is found first and foremost in the Creator, blessed be he, as the psalmist says (Psalms 89, 15): "Kindness and truth will march before You". Our Sages of blessed memory said in the Midrash (Bereshit Raba 8): "Rabbi Samlay said: we find that the Holy One, blessed be He, blesses bride grooms etc." and He brings there proofs for all these from the Bible. They further said about the verse (Deut. 13, 5) "Follow Hashem's ways" (Talmud Bavli, tractate Sotah 14a): "Just as He is merciful, be merciful etc.". And in (Talmud Bavli, tractate Sukka 49b): "Our Sages taught that kindness is greater than Tzedakah1 in 3 particulars: kindness is carried out with one's body and possessions etc.". From this they taught us that this virtue comprises both spiritual and material forms of kindness as we said above, as it is said (Proverbs 11, 17): "He who takes care of himself is a kind person and he who neglects himself is a cruel person": this is true in both spirit and body.
This trait of kindness is found in the animal world in the fowl called Ipega2: when these birds see that their parents are aging and losing their eyesight and becoming week, they toil and prepare a nest for them and bring them their food; and with their beak they pluck those feathers, in particular around the eyes, which hinder their sight, until new feathers sprout naturally and their sight returns.
Even though this behavior stems more from honoring one's parents than from kindness in the broader sense, nevertheless they do this only out of compassion resulting from kindness, and we have already explained what is the nature of kindness. And those who have compassion for others will receive compassion in the words of [king] Solomon (Proverbs 21, 13): "The person who ignores the cry of the unfortunate will find no response when he will cry out".
Alexander said: "A person will increase his influence in three ways: by acquiring friends; by having compassion for others; by forgiving enemies."
This trait also involves conducting one's affairs beyond the letter of the law: one who does this will be called devout. He will also overlook all affronts.
Pythagoras said: "If your hand will hurt your eyes and your teeth will cause pain to your tongue, you wouldn't dream of taking revenge, since they are all parts of yourself: so you should treat your fellow man".
Plato said: "If man took revenge on every form of wrongdoing committed upon him, his Lord would very quickly return the world to its original chaos".
Seneca said: "Imagine that you have already taken revenge as much as possible, and in that way you will forgive your enemy".
The world only exists as a result of Kindness, as it is said (Psalms 89, 3): "I said that the world will be built on kindness3".
Notes of the translators:
 Tzedakah is a major Mitzvah which stems from the connection between two principles: charity and justice (as in Tzedek, the Hebrew root of the word Tzedakah). See also the use of the term Tzaddik to indicate the righteous person.
 Probably a kind of crow.
 The author interprets this verse according to the subject of our chapter and in line with Midrashic sources. Other commentators suggest an alternative interpretation, which says that kindness will last forever.
The whole book Tzemach Tzadik in Hebrew, written by Rabbi Aryeh Yehuda Leone di Modena (printed in Rashi characters) can be downloaded in PDF format and read online at Hebrewbooks.org. Chapter 12 about kindness is found at pages 25-27.