Back in the late 70s, when I was working on my dissertation on religious-metaphorical language and speaking about God and religious experience, the work of University of Chicago theologian Langdon Gilkey was important. Especially his book Naming the Whirlwind: The Renewal of God-Language. (Selling now, used at amazon, for $.01) Today I'm prepping for this coming Sunday's sermon out of 2 Corinthians 6:14-18. Hughes quotes from Gilkey, on the condition of the Church in America. Hughes quotes from Gilkey as an example of Paul's concern for the Corinthian Jesus-followers and their unequal-yokedness with pagan religious rituals and ideas.
"All around us we see the church well-acclimated to culture; successful, respected, wealthy, and growing. But are the transcendent and the holy there? In the area of belief we find widespread indifference to the Bible and igorance of its contents - and strong resentment if a biblical word of judgment is brought to bear on the life of the congregation. In worship we find notably lacking any sense of the presence of God and of what worship is for... In ethics we find the cultural ideas of friendliness and fellowship more important than the difficult standards of the New Testament or historic Christendom." (Hughes, 2 Corinthians: Power in Weakness, K 2621; from Gilkey, How the Church Can Minister to the World Without Losing Itself - also selling, in hardcover, for $.01 at amazon.)
It's about set-apartness, also called "holiness."
14Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness? 15What harmony is there between Christ and Beliar? What does a believer have in common with an unbeliever? 16What agreement is there between the temple of God and idols? (2 Cor. 6:14-16)