Musar su Salmi 111:3

One day one of the great scholars of that generation, Rabbi Chaim Vital, came before him. The Ari told him, “I see that that all twenty-two of the letters on your forehead are illuminated with the exception of the letter gimmel, which is backwards.” Upon hearing this Rabbi Chaim Vital was filled with trembling. He asked the Ari z”l to reveal to him why this was so, for it was surely not in vain! The Ari answered that Rabbi Chaim had not performed sufficient acts of kindness towards his father. “Although you do perform acts of kindness towards him they are not complete and for this reason the gimmel is backward.” The Ari revealed further that whenever a person performs one of the commandments it is recorded upon his forehead with one of the twenty-two letters of the alphabet. If he then performs the same commandment a second time the letter begins to shine. For the first time he performs it the letter remains sunken into the skin, but the second time it stands out and sparkles. This is true of all the commandments with the exception of charity, which is not sunken into his skin like the others but shines forth immediately upon his forehead as is hinted at in the verse, “And his charity enures forever” (Tehillim 111:3).

David goes on to say: הודו, "give praise," an allusion to Lamentations 1,13: כל היום דוה, "in misery all day long" (constantly). The Zohar, in understanding the "day" as the day of G–d's timetable, i.e. 1000 years in our reckoning – as we have explained on several occasions – feels that the present exile was decreed for a minimum of 1000 years. This period could prove fatal for the Jewish people as alluded to when you reverse the letters in the word הוד i.e. דוה. When the Psalmist states in Psalms 96,6: הוד והדר לפניו עוז וחדוה במקומו, according to our sages, the word הדר is derived from the word הדרן, "review or reversal. If our actions are "good," then the result is הוד; if they are "evil," the result would be דוה, ongoing misery. Either way, all this happens in His Presence, i.e. G–d arranges that even the "evil" will eventually turn into good, i.e. the result of דוה will eventually be הוד, praise of G–d. I have explained this in greater detail elsewhere. The idea that הוד is reversible is expressed very clearly in Daniel 10,8: והודי נהפך עלי למשחית "My splendor turned into a destructive force."