Musar su Deuteronomio 15:8

When the Torah goes on כברכת ה' אלוקיך this is a warning that we should not think that G–d's "blessing" is something He grants without any input from us. G–d does not "give" a blessing. When man on earth performs "blessed" deeds, he activates the blessing which lies in wait in Heaven. The blessing that man appears to have received from G–d is actually something that is the direct result of his own activities. When the Torah directs (15,8): פתח תפתח את ידך, "Keep opening your hand, etc.," the message is that G–d will open His heavenly treasure chamber in direct relation to the number of times we have opened our hands to the poor down here on earth. Keeping such considerations in mind we will surely fulfil the commandment to be charitable in the proper spirit.

There is a deep significance in the fact that the two words כף and פך consist of the same letters. The only difference between them is that the letter כ in the word כף is כפופה, bent over, closed, whereas the same latter in the word פך is open. The former shape is an inferior one, as it alludes to a closed palm, someone who is tight-fisted. The letter פ alludes to the mouth above. When the letter ך is open, it reminds us of open-handed charity, i.e. פתח את ידך, "open your hand." Having opened one's hand, it is important to keep one's mouth closed as indicated by the shape of the letter פ, when it is כפופה, closed. There is no greater virtue than silence (Avot 1,17). Thus the combination of an open ך, and a closed פ, is an excellent one. Both Joseph and the brothers committed an error. Joseph talked too much by bringing evil gossip about his brothers to his father (37,2). The brothers erred by being greedy for money and stooped low enough to sell their brother Joseph for twenty pieces of silver.