'REliezer ben Yaakov says: He who fulfills [even] a single mitzvah acquires for himself a single advocate, while he who commits [even] a single transgression acquires for himself a single accuser.  Repentance and good deeds are like a shield against mis-fortune.  R' Yochanan HaSandler says: Every assembly that is dedicated to the sake of Heaven will endure; but one that is not for the sake of Heaven will not endure.