The Hebrew letter Shin has three prongs and represents the indivisible unity of G-d, Torah, and Israel. On the Tree of Life it represents “Hokhmah” or wisdom and is located in the right hemisphere of the brain. Wisdom comes from the Holy One in a flash and is indivisible and indescribable.
The left hemisphere of the brain, however, is created by G-d in order to “figure things out” and to to attempt to divide the indivisible and to describe that which is beyond words. This gift is called “Binah” and translates into English as understanding. In Kabbalah it is represented by the Shin with four prongs, as represented here. Why four? Because four is a divisible number and represents the aspect of intellect which is linear, orderly, and verbal.
The two Shins represent the male and female energies that Hashem has created. The three-pronged Shin is for Abraham, Isaac, and Jacob. The four-pronged Shin is for Sarah, Rebecca, Rachel, and Leah. There are thirteen letters in the names of the patriarchs (Abraham, Issac, and Jacob) in Hebrew, and there are thirteen letters in the names of the matriarchs (Sarah, Rebecca, Rachel, and Leah). G-d’s most holy name (called the Tetragrammaton) has the gematria (numerical value) of twenty-six which is the unity of the fathers and mothers, the masculine and feminine principles in the universe. Finally, four and three add up to seven which represents completion and totality as in the days of the week.