Why does James believe that his mother's  practices represented the best and worst of the immigrant mentality?

Ruth's motherly governance over twelve children in the housing projects of Brooklyn, according to James, expressed her own strict Orthodox Jewish upbringing: "unbending nature, a stridency, a focus on money, a deep distrust of all outsiders, not to mention her father's tyranny - [they] represented the best and worst of the immigrant mentality: hard work, no nonsense, quest for excellence, distrust of authority figures, and deep belief in God and education." Though she consciously cast off her Jewish identity, it remained a distinct part of her largely because it was a part of her experience. Her upbringing was the only model she had to work with when she raised her children, so she could not dislodge herself from her identity (and history) completely. What was once a part of her history was forever a part of her future. James implies that the secret to the success of each of Ruth's twelve children, in other words, was something rooted in the mysterious alchemy of growing up under the influence of the immigrant mentality, along with the communal nature of the house and the black community in general.