The Jews were told in the book of Deuteronomy not to mix with other nations because if they did they would no longer be pure. Even so the mixing between church and the world can not co-exist. There has to be a separation between holy and unholy, clean and unclean. In this day and the time the church is living so close to the world until everything is running together and the lines are blurred, in other words our lifestyles, are mimic the lifestyles we lived before coming to Christ and it's confusing the unbelievers. But today God is calling us to make a difference or a separation, so the world cand see the difference and will compel them to come to Christ! If we get in the word and then allow the to get in us, things will become clear, our lifestyles will become clear and there will be no more blurred lines.