2 Corinthians 10:3

Walk in the flesh. That is, live in this world as a human being.

War after the flesh. Though living among men who resort to worldly methods, Paul does not condescend to do so. Compare Christ’s words about His followers being “in the world” but “not of the world” (John 17:11, 14). The converted man possesses an entirely new and different nature, and is motivated by the above love of Christ and the Spirit of God, in harmony with divine ideals (John 3:3, 5; Rom. 8:5-14; 1 Cor. 2:12-16; 2 Cor. 5:14). He has gained the victory over the world, the flesh, and the devil (see 1 John 2:15, 16). With the experience of regeneration and the new birth, there exists at once an active and inveterate hostility and war between flesh and spirit (Rom. 8:3-14; Gal. 5:16-23). The two cannot be united. The flesh can never become spiritual. In it “dwelleth no good thing” (Rom. 7:18). The Christian is still in the world, but his spiritual nature predominates over the lower, fleshly nature (see Rom. 1:18 to 2:4). Paul fights the good fight of faith with spiritual weapons, not those of the world (Eph. 6:12-20). Paul understands the true nature of the situation at Corinth, and will not hesitate to use these weapons as the situation may require.