Collateral damage is injury inflicted on something other than an intended target.
As Christians, we are warned not to be unnecessarily close to unbelievers. One scripture is “be not unequally yoked to unbelievers”. For example, a Christian is not supposed to marry an unbeliever even if he or she is drowning in love. Why is this so?
1 Samuel 15:6
“And Saul said unto the Kenites, Go, depart, get you down from among the Amalekites, lest I destroy you with them: for ye shewed kindness to all the children of Israel, when they came up out of Egypt. So the Kenites departed from among the Amalekites.”
God instructed Saul to destroy the Amalekites because they had been hostile to the Israelites. One way God executes judgments is by using other people as instruments of judgments. The Kenites, another tribe which had been kind to Israel were friends with the Amalekites and were living amongst them. Saul adviced them to separate themselves otherwise they will also be destroyed and be victims of collateral damage.
Unbelievers can easily attract the judgment of God because of their rebellion. A certain close association with them can make us victims of collateral damage in the day God executes his judgment.
Do you want to avoid collateral damage? Be ye not unequally yoked together with unbelievers.