Live in harmony

‘Live in harmony with one another. Do not be proud, but be willing to associate with people of low position. Do not be conceited.’ Romans 12:16

I don’t find the last part difficult. Don’t believe I’m particularly proud or conceited and I mix with all types of people. The difficulty I find is to always live in harmony. I find it difficult to understand why people do not believe in God or dismiss His existence. There is so much evidence and I fear for their final destination.