Cutting Fingernails

Why is there an emphasis on cutting fingernails before Shabbat?

Shalom!

Thank you for your question.

Indeed, it is commendable to cut one's fingernails on Friday afternoons in honor of Shabbat. (1) We are taught that one should not cut them in the order of one's fingers, (2) one after the other as doing so is said to lead to forgetfulness and bad luck. (3) So too, since the fingernails of the dead are cleaned and cut one after the other in preparation for burial, we should cut our fingernails out of order.

The recommended order for trimming one’s nails on the left hand is: the fourth finger, followed by the second, fifth, and third fingers, concluding with the thumb. When trimming the nails on the right hand, the order is: the second finger, followed by the fourth finger, the thumb, and the third finger, concluding with the fifth finger. The same halacha is when cutting one's toenails. (4) According to the Ari there is no particular order in which the fingernails are trimmed. (5) (6)

Some sources advise against trimming one's fingernails on Wednesday from shekiah till shekiah on Thursday as the fingernails start to regrow three days after having been cut. This would mean that one’s nails would begin growing again on Shabbat. As such, trimming one’s nails on Thursday might be viewed as if one is arranging for a forbidden act to take place on Shabbat. (7) It is also explained that fingernails don't look nice and tidy when they begin growing again and, therefore, this would actually take away from the honor of Shabbat. 

We are taught that one will be rewarded for ensuring that one's hair and nails were always trim and tidy in honor of Shabbat. (9)

1. OC 260:1.

2. Kaf Hachaim, OC 260:17.

3. Machzor Vitri 524; Sefer Kushiot 166.

4. Rema, OC 260:1.

5. Tashbetz 5:57; Shulchan Aruch Ha'arizal 260:10; Kaf Hachaim (Palagi) 27:15.

6. Ketzot Hashulchan 73:7.

7. Mishna Berura 260:6.

8. Kaf Hachaim, OC 260:15.

9. Kaf Hachaim, OC 206:16.