What book teachs one how to overcome the negative influences of those around them & yet still be a part?

ans still be a part of the world rather than shun it? Mother Theresa didn't say "Lepers could make me sick so I better not go around them". So what was it about her besides her strong faith that kept her in the mix of life. I want to strenghten my mind so I can believe what I believe & not need others to agree with me & yet not feel put down when they disagree so much withmy beliefs.