The Torah relates that Abraham and Sarah's son was named Isaac (יצחק). This name was directly indicated by God, as it is written in Genesis 17:19, "And you shall call his name Isaac." This name is related to the joyful laughter that Abraham, at 100 years old, felt upon hearing the news that he would have a son with his wife Sarah (who was 90 years old). See Genesis 18:12-15.
In turn, our sages explain in many places that each patriarch corresponds to a divine quality: Abraham with kindness (Chesed), Isaac with severity (Gevurah), and Jacob with mercy (Tiferet).
We see, then, that there is a relationship between severity and joy. We also find that the name Yitzchak (יצחק) is written with the letter Sin (ישחק) four times throughout the scriptures. To explain this, here is a free translation of a portion of a commentary by Rabbi Yehuda ben Yosef Moscato (c. 1530 – c. 1593), born in Osimo and died in Mantua, Italy.
Nefutzot Yehuda, End of chapter 23:
(https://hebrewbooks.org/6084)
And now, let our hearts be lifted up to our hands, to rejoice and be worthy to elevate the quality [of judgment] to mercy, and God would again rejoice in us for good, and make us drink the four cups of comfort, alluded to in the four cups of Passover, as explained in the Jerusalem Talmud, and redeem us from the four reigns alluded to in them, as mentioned there.
And for this reason, we find the name Isaac (ישחק) four times in the scriptures with Sin (ש): once in Jeremiah (33:26), “To the offspring of Abraham, Isaac and Jacob, when he restores their fortunes and has mercy on them”; twice in Amos (7:9), “and the heights of Isaac shall be destroyed”; (7:16), “And do not prophesy against the house of Isaac”; and the fourth time in Psalms (105:9), “Who made a covenant with Abraham, and his oath to Isaac,” to indicate that from Isaac, which alludes to the quality of judgment, came to us all the suffering written with the letter Tzadik (צ). And in the future, it will be changed and transformed into a letter Sin (ש), which contains the allusion to joy and rejoicing.
Grades:
- It is clear that the coming of Mashiach depends, to some extent, on transforming the bitterness of exile into sweetness, and this is alluded to by the four times the name Isjak (ישחק) appears in the scriptures.
- The relationship between the letter Tzadik (צ) and the quality of Gevurah (severity) could be said to come from the fact that the letter Tzadik is one of the 5 double letters (מנצפ"ך), that is, final letters of words in the Holy Language which, in turn, are directly related to Severity (Etz Chaim Shaar 28, Drush 2)