We are in the world, not called to be part of the world. Coexistence leads to syncretism.
Definition of: syncretism
1. the amalgamation or attempted amalgamation of different religions, cultures, or schools of thought.
A Few verses from scripture:
Deuteronomy 7:3, Joshua 23:7, Joshua 23:12, Jeremiah 10:2, 2 Corinthians 6:14