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. This line divided God’s people in Goshen from the rest of Egypt.
“The Lord will make a difference between the livestock of Israel and the livestock of Egypt. So nothing shall die of all that belongs to the children of Israel. For at this time I will send all my plagues to your very heart, and on your servants and on your people, that you may know that there is none like me in all the earth” (Exodus 9:4,14).
God wants everyone to see the difference between those who love him and the rest of the unbelieving world. He wants us to be an example of a delivered, trusting and victorious people.
The reasons for separation today are the same as they were in ancient times. In every generation, God draws a line that shows the stark difference between righteousness and wickedness. Nothing else fully captures the attention of those who disobey and brings them to repentance.
Jesus said, “I chose you out of the world, therefore the world hates you” (see John 15:19). The world loves its own, but under the New Covenant we have been reborn. We are new creatures in Christ Jesus from a different world. May he help us joyfully embrace this unique and wonderful position! Only those who are truly unmixed with the world, separated unto Christ, have any power to save it. “Do not love the world or the things in the world. If any man loves the world, the love of the Father is not in him” (1 John 2:15).