Q:I have been told that an advocate begotten of one man's good deed may guide another man in choosing rightly, while an adversary spawned by an evil deed will seek out vulnerable individuals to lead them astray. Is this simply an extended parable to the effect that our choice of good or evil will influence others to choose as we have, even if we believe we act in private and our choice is known to us alone?
A: What you were told relates to the Mishna, Pirkei Avot, the Ethics of our Fathers, (chapter 4:11):
Rabbi Eliezer ben Yaakov said: He who fulfills one mitzvah acquires for himself one advocate, and he who who commits one transgression acquires against himself one accuser. Repentance and good deeds are as a shield against retribution.
The Mishna does not explicitly say that these two spiritual, angelic powers may influence others. The simple meaning of the Mishna is that it only relates to the person himself. The continuation of the Mishna says that returning to G-d and repentance for evil deeds, and the good deeds that one subsequently does, serve as a shield in the face of punishment. Even though a person has done evil, and has accusers, they can be nullified and eradicated by repentance and good deeds. Even if accusers are not totally eradicated, the person creates a shield which surrounds him and protects him from their evil influence.
Since all Jewish souls are "guarantors" for each other it is clear that every act that an individual Jew does, directly or indirectly affects all other Jewish souls. Every Jew is related to all other Jews, just as the limbs of the body affect one another. This explains the importance of helping fellow Jews to find the proper way of life, to return to G-d and to do good deeds. When one Jew chooses the proper path, he brings goodness to all other Jews, and ultimately to the entire world.