1It is actually reported that there is sexual immorality among you, and such sexual immorality as is not even named among the Gentiles, that one has his father’s wife. 2You are arrogant, and didn’t mourn instead, that he who had done this deed might be removed from among you. 3For I most certainly, as being absent in body but present in spirit, have already, as though I were present, judged him who has done this thing. 4In the name of our Lord Jesus Christ, when you are gathered together with my spirit with the power of our Lord Jesus Christ, 5you are to deliver such a one to Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
6Your boasting is not good. Don’t you know that a little yeast leavens the whole lump? 7Purge out the old yeast, that you may be a new lump, even as you are unleavened. For indeed Christ, our Passover, has been sacrificed in our place. 8Therefore let’s keep the feast, not with old yeast, neither with the yeast of malice and wickedness, but with the unleavened bread of sincerity and truth.
9I wrote to you in my letter to have no company with sexual sinners; 10yet not at all meaning with the sexual sinners of this world, or with the covetous and extortionists, or with idolaters, for then you would have to leave the world. 11But as it is, I wrote to you not to associate with anyone who is called a brother who is a sexual sinner, or covetous, or an idolater, or a slanderer, or a drunkard, or an extortionist. Don’t even eat with such a person. 12For what do I have to do with also judging those who are outside? Don’t you judge those who are within? 13But those who are outside, God judges. “Put away the wicked man from among yourselves.”
Deut 12:2 "Ye shall utterly destroy (חרם, ḥērem)" -Israel is supposed to be totally separate culture from those around them.
The passage here is much about the centralization of worship in Deuteronomy, and as such a very important topic in academic discussion in Old Testament scholarship for the last 200 years. Without going here into any of the complications and various opinions expressed, according to Deuteronomy’s vision, Israel is to gather together in one place for worship three times a year, and sacrifice their offerings only in that place. In a broader context, this is to happen when the nation has settled in the land and is at peace, and such travelling is possible in practice (Deuteronomy 12:10-11). In other circumstances, one may sacrifice locally (cf. Exodus 20:22-24; cf. Deuteronomy 27; Joshua 8:30-35; note however that, according to Leviticus 17:1-9, during the time in the wilderness, all sacrifices had to be brought to the tent of meeting, the Israelite sanctuary at the time). In a yet broader context, the concern of Deuteronomy, and the Pentateuch and Old Testament as a whole is that the Israelites worship only their God Yahweh. From another angle, as part of the settlement and striving towards purity in life and worship, the indigenous nations and their worship practices are to be eradicated so that no trace is left to lead Israel astray.
In modern thinking, the command in Deuteronomy actually amounts to genocide and is therefore problematic, particularly for those who take a high view of Scripture, and raises the question of theodicy, or the justification of God’s actions. But, if one reads the book of Revelation or even the New Testament as a whole, the apparent concept of damnation to unbelievers is at least arguably in line with the concept of killings of non-Yahwists in the Israelite conquest tradition. The issue at hand here is also perhaps mitigated by the fact that the Israelites did not manage to drive out or kill many of the native inhabitants, and by the fact that the conquest and settlement are to be considered as a one-time non-repeatable set of events.
All this said, as the nations were left in the land, as the Bible describes, the Israelites started to follow their practices (see the book of Judges in particular). These points considered, for Christians the passage can be read to promote fleeing away from idolatry and from any practices that are contrary to good Christian ethical principles, in line with New Testament material (cf. 1 Corinthians 10:14). The New Testament also seems to ask Christians to think of whom they associate with (1 Corinthians 15:33), and yet, this does not mean that one cannot associate with those who are not Christian (1 Corinthians 5:9-11). Jesus himself associated with all, and the Pharisees who criticised him for that are described as hypocrites by the New Testament (see e.g. Matthew 9:9-13, 22:18, note also that Paul in 1 Corinthians 15:33 might be quoting a popular proverb of the time). So, great wisdom and humility is required of Christians in following God with joy and ethical verve, while at the same time refraining from dubious practices without becoming haughty, condescending, or even violent towards others.