Likutei Moharan, Part II 4:1/ליקוטי מוהר"ן·תנינא ד׳:א׳

1“On the day of the first fruits, when you bring an offering of new-meal to God on your Shavuot Festival, you shall observe an occasion proclaimed sacred; you shall not do any mundane work.” (Numbers 28:26)

2“V ’et HaOrvim Tziviti LeChalkelekha (And I Have Commanded the Ravens to Feed You)” (1 Kings 17:4)—this alludes to charity. Initially, when a person begins donating charity, he has to break his heartlessness and turn it into compassion. This is the essential devotion of charity. When someone naturally compassionate gives charity purely out of his compassionate instinct, it is not an act of devotion—there are <also animals> that are compassionate by nature. Rather, the essential devotion is transforming cruelty into compassion.

3This is the meaning of “And I have commanded the ravens to feed you.” The raven, cruel by nature, turned compassionate in order to feed Eliyahu. It must be the same with charity. And even those who are benevolent—all who are generous must first undergo this process of “And the ravens.” In other words, in order to donate charity they first have to break their heartlessness—their initial tendency to be cruel—and turn it into compassion.