Paul’s use of this phrase in 2 Corinthians 6.14 is an illustration taken from Old Testament prohibitions to Israel regarding the work-related joining together of two different kinds of livestock (Deut. 22.10). By this analogy, Paul taught that it is not right to join together in common spiritual enterprise with unbelievers—a relationship that would be detrimental to the Christian’s testimony within the body of Christ. It is impossible under such an arrangement for things to be done to God’s glory (1 Cor. 5.9–13; 6.15–18; 10.7–21; James 4.4; 1 John 2.15). This was especially important for the Corinthians because of the threats from the false teachers and the surrounding pagan idolatry. But this command does not mean believers should end all associations with unbelievers. That would defy the purpose for which God saved believers and left them on earth (Matt. 28.19, 20; 1 Cor. 9.19–23).
“And what accord has Christ with Belial?” (v. 15). An ancient name for Satan, the utterly worthless one (Deut. 13.13). This contrasts sharply with Jesus Christ, the worthy One with whom believers are to be in fellowship. “And what agreement has the temple of God with idols?” (v. 16). The temple of God (true Christianity) and idols (idolatrous, demonic false religions) are utterly incompatible. “You are the temple of the living God.” Believers individually are spiritual houses (5.1) in which the Spirit of Christ dwells. “As God has said.” Paul supported his statement by referring to a blend of Old Testament texts (Lev. 26.11, 12; Jer. 24.7; 31.33; Ezek. 37.26, 27; Hos. 2.2, 3).
Paul drew from Isaiah 52.11 and elaborated on the command to be spiritually separated. It is not only irrational and sacrilegious but disobedient to be bound together with unbelievers. When believers are saved, they are to disengage themselves from all forms of false religion and make a clean break from all sinful habits and old idolatrous patterns. “Be separate.” This is a command for believers to be as Christ was (Heb. 7.26).