The most insignificant people are the most apt to sneer at others. They are safe from reprisals. And have no hope of rising in their own self esteem but by lowering their neighbors.

This quote means that people who feel insignificant and powerless in comparison to others often choose to belittle them instead of building themselves up in a positive way. Because they are powerless, they are safe from any consequences and can only feel better about themselves by making others feel worse.