When we spy or eavesdrop on someone, we are trying to gain information that is not being willingly shared with us. There are many cases in which eavesdropping or spying is a sin. But in other cases there may, in fact, be legitimate reasons to spy or eavesdrop.
Spies are employed by governments as a part of their national security. Without spying on enemy plans, a nation could lose its freedom. During times of war, spying on the enemy and collecting military intelligence have been crucial to victory. God told Moses to send spies into the land of Canaan to learn what the Israelites were facing in taking it (Numbers 13:1–2). Later, Joshua sent spies into Jericho before that decisive battle (Joshua 2:1). In Judges 7:9—15, God instructed Gideon and his servant Purah to spy on the Midianites.
Eavesdropping, secretly listening to a private conversation, is a violation of privacy and often a breach of trust. But eavesdropping also has its place. It could have been eavesdropping that prevented the murder of Paul (Acts 23:16) and thwarted the assassination of King Xerxes (Esther 2:21–23). As a modern example, a mother concerned about the direction her teenager is going may pause outside the bedroom door when she hears her daughter on the phone. The words drinking and party catch her attention. Because she has her daughter’s best interest in mind, she may eavesdrop in order to know how to protect her child. So spying and eavesdropping are not wrong in themselves. The sin lies in the purpose behind the action.
When we spy or eavesdrop due to selfish motives, we are crossing a line. Envy, jealousy, or desire for revenge may wrongly motivate us to eavesdrop or spy on someone. If our intent is to use the information gained to give ourselves an unfair advantage or to harm someone else, then eavesdropping is wrong. It is dishonest and unloving (Romans 13:8; Luke 6:31). Christians are to be “blameless and innocent, children of God without blemish in the midst of a crooked and twisted generation” (Philippians 2:15). Eavesdropping out of nosiness is being sneaky, which is dishonest (Proverbs 11:3). If we hear something juicy, we often don’t want to keep it to ourselves, so eavesdropping becomes the first step to gossiping.
On those occasions when spying or eavesdropping is done with altruistic motives, then it is allowable. But any hint of selfishness, egoism, or voyeurism taints it with sin. If in doubt about the virtue of spying or eavesdropping in any given situation, we should always default to Jesus’ words in Luke 6:31: “Do to others as you would have them do to you.”