There is nothing in the Old Testament quite as strong as the warnings of Paul against affinity with the world:
“Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? And what accord has Christ with Belial? Or what part has a believer with an unbeliever? And what agreement has the temple of God with idols? For you are the temple of the living God. As God has said: I will dwell in them and walk among them. I will be their God, and they shall be My people” (2 Corinthians 6:14-16 NKJV).
In the Old Testament, when God wanted to reveal the power of his presence before the wicked Egyptians, he drew a line of separation, dividing God's people in Goshen from the rest of Egypt.
“And the Lord shall sever between...Israel...and Egypt...For I will at this time send all my plagues upon thine heart...that thou mayest know that there is none like me in all the earth" (Exodus 9:4, 14).
God wants the world to see the difference between his people who love him and the rest of the unbelieving world. He wants us to be an example of a delivered and victorious people, trusting in his mighty arm to deliver us from all harm and evil.
The reasons for separation from the world (Egypt) today are the same as they were in ancient time. God is once again drawing a line between his people and this wicked age, so that this generation can know there is none like him to deliver in all the earth. The wicked of this age must have an even greater manifestation of the Lord's presence; nothing else will get their attention. Nothing else will smite them with conviction for sin. The Holy Spirit has been outpoured, so that all flesh could come under the power of Christ's presence and be convicted of sin, righteousness, and judgment!
Speaking of his true disciples, he said, "They are not of the world, even as I am not of the world" (John 17:16). Again, "I have chosen you out of the world, therefore the world hateth you" (John 15:19).
The world loves its own, but we are not of the world. May God help us to joyfully accept our special character of separation and difference. Only those who are truly unmixed with the world, separated unto Christ, have any power to save it!
"If any man love the world, the love of the Father is not in him" (1 John 2:15).