The following is an excerpt from The MacArthur New Testament Commentary on 2 Corinthians 7 .

Therefore, having these promises, beloved, let us cleanse ourselves from all defilement of flesh and spirit, perfecting holiness in the fear of God. (2 Corinthians 7:1)

Having God’s promises provides powerful motivation for believers to separate from unbelievers. Paul’s use of the word therefore is a call for action based on what he has previously written (cf. Rom. 12:1–2; 2 Peter 1:3–8). The apostle moves beyond the commands of 2 Corinthians 6:14, 17 and appeals to God’s promises enumerated in 6:16–18. Those promises should elicit love, gratitude, and thankfulness for His overwhelming generosity. In fact, one of the things that characterizes unrepentant sinners is ingratitude (Luke 6:35; Rom. 1:21; 2 Tim. 3:2)

The endearing term beloved (cf. 2 Cor. 12:19; Rom. 1:7; 12:19) defines who God’s promises apply to. Only His beloved children, accepted by Him because of their union with His beloved Son (Eph. 1:6; Col. 1:13), receive God’s promises.

Paul defined the appropriate act of gratitude in both negative and positive terms. Negatively, believers must cleanse themselves from all defilement of flesh and spirit (cf. Isa. 1:16; James 1:21). The reflexive pronoun heatous (ourselves) indicates that though the cleansing work is God’s (cf. Acts 15:9; Eph. 5:26; Titus 3:5), it does not happen apart from believers’ effort (cf. Phil. 2:12–13). Molusmos (defilement) appears only here in the New Testament. In all three of its uses in the Septuagint, however, it refers to religious defilement. Paul calls believers not only to cleanse themselves from sin and immorality but especially, in this context, from all associations with false religion. That complete cleansing is to be both of flesh and spirit; that is, both inward and outward. False teaching defiles the whole person by pandering to sinful human appetites and corrupting the mind. Therefore, believers must avoid both the fleshly sins and the pollution of the mind that false religion brings.

Positively, cleansing oneself from false religion involves perfecting holiness in the fear of God. Perfecting is from epiteleo, which means, “to finish,” “to complete,” or “to fulfill.” Believers are to pursue the goal of holiness (Lev. 20:26; Matt. 5:48; 1 Peter 1:16) by separating from all the lies and deceptions that would defile them, encouraged by the hope that the goal will someday be achieved (Phil. 1:6; 1 Peter 5:10; 1 John 3:2). Motivating believers’ pursuit of holiness is the reverential fear of God, which is foundational to godly living (Job 28:28; Pss. 19:9; 34:11; Prov. 1:7; 8:13; Acts 9:31).

The church must confront the world to fulfill the Great Commission given to us by our Lord (Matt. 28:19–20). Yet we must not compromise with false religion to do so. To disobey God’s explicit command to separate from unbelievers is foolish, blasphemous, ungrateful, and forfeits God’s blessing.