129. The fingers of man represent the most hidden of all grades and secrets of the supernal world, and are divided into front and back. The back of the fingers represents the external part, an allusion to the fingernails. As such, man may look at his fingernails as Shabbat ends. As they shine by the candlelight and are bright from that fire, that rules OVER THE DAYS OF THE WEEK.
130. THE FINGERNAILS are visible, but it is not permissible to see the inner part of the fingers by this candlelight, because they shine only from above. And THE INNER PART OF THE FINGERS is called the inner face. This is the secret of the verse: "And you shall see My back; but My face shall not be seen" (Shemot 33:23), which means that a person should not look at the inside of his fingers at the end of Shabbat, as he recites the blessing: 'Creator of the luminaries of the fire (Heb. bore me'orei ha'esh)'. The phrase: "And you shall see My back" refers to the external part OF THE FINGERS, which is hinted at in the fingernails AND SHINES AS SHABBAT ENDS. "But My face shall not be seen" refers to the inside of the fingers, WHICH CANNOT RECEIVE FROM THE LUMINARIES OF THE FIRE. THE INTERNAL PART OF THE FINGERS rules on Shabbat. THE EXTERNAL PART OF THE FINGERS rules during the weekdays.