Answer:
   
   In Judaism, one's name has always been considered to be extremely
   important. As names were bestowed, the meaning of the name was the
   prime consideration of its selection. The name often imbodied
   characteristics that the parents wished the infant to have, or
   experiences surrounding the birth, or the look of the infant.
   
   Many naming traditions in Judaism arose out of custom, and this custom
   often arose out of superstition. This was often based on a close
   association between the name and the person. From this arose a common
   belief that the changing of a name would prevent the evil spirit from
   harming the person. If the name were changed, the evil spirit would
   not recognize the person. This belief is embodied in the Talmud (Rosh
   Hashanah 16b): "Four things can abrogate the decreee of man and they
   are: charity, supplication, change of name, and change of action."
   
   These customs carried over in Eastern Europe to the naming of
   children. In Poland, when several people have died in a family, a
   new-born child is given a name that is never uttered, so as not to
   give the evil spirit any opportunity. Often, a nickname was given to
   the child, such as "Alte" (Old One), Chaim (Life), or Zaida
   (Grandfather). This was a way of deceiving the angel of death. A
   similar practice was done for the extremely ill, changing the
   individual's name to deceive the angel of death.
   
   In Ashkenazi Judaism, the custom arose to name a child after a
   deceased relative. Infants were not named after the living, because
   the angel of death might mistake the infant for the adult, and take
   the wrong one. Some felt that to name after a living relative might be
   to rob the adult of their soul, as the name was tied very closely to
   the soul.