Believers are commanded not to love the world, which is the system ruled by Satan (i John 2:15-19). No one can love both the world and also love our Heavenly Father. Believers are to respond to the lusts, or carnality, of the world with the world (II Corinthians 6:11-18), and He cautions believers not to get caught up in worldly lifestyles. Friendship with the world is "enmity with God" (James 4:1-4). However, there are those who appear to be in the Body, but are false brethren because they do not continue in God's ways. Christians who are developed in the Word of God will recognize the distinction. We as believers are to have fellowship - the act of social intercourse or the coming together with one another = but not be in covenant with unbelievers. Their evil company, or carnal ways of living, will corrupt the godly habits of Christians (I Corinthians 15:33). Holy living separates the believer from the unbelievers. However, when sinners encounter the light of the gospel in believers, they will follow them.