I wrote unto you in an epistle not to company with fornicators: Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.
-1Co 5:9-10
To keep company means any kind of assembling together with people. As you can see if you continue to read 1Co 5, what we need to be careful of is assembling together with anyone who calls himself a "Christian," but lives in his sin.
But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
-1Co 5:11
It is not that a Christian cannot or will not sin, but the problem is the lack of repentance of sin in a person who calls himself Christian; meaning that a man will claim to be of Christ and seek not to turn from his sin.
The major focus you should have is over the word fellowship, which can mean "company" depending on the context, but where as 'company' seems to be more along the line of assembling together with others for an event (and in 1Co 5, it is meant specifically that we do not assemble together with others for religious purposes with those who live according to their sins), but 'fellowship' seems to be more "companionship" or "familiar intercourse," which is the closeness of friendship with others.
And have no fellowship with the unfruitful works of darkness, but rather reprove them.
-Eph 5:11
The problem I have seen is that a number of Christians, even some in our own church, still kinda' "ho-hum" this one, meaning they do not pay much attention to it. We can help others in charity, we can speak to them and try to tell them the truth, we can be kind to them, but we are not supposed to be hanging out with them in what Noah Webster (if I may borrow from his 1828 dictionary) called "mutual association of persons on equal and friendly terms."
This is not talking about buying groceries at the same store, or being employed (or servants) at the same job. The focus of our assembly should be with the church, that is, with born again and sanctified Christians together, and sadly, some still ignore this in the New Testament.
And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.
-Heb 10:24-25
As our church can testify (at least, those who have accounts here and read this on a regular basis), I have never pushed this on anyone in the church. I have only taught it briefly in times past, and I let the Holy Spirit work in each to understand these things, or rather, to understand WHY this is important.
To be... I guess I would use the word "chummy"... or intimately familiar with those who are unbelievers and/or the wicked who walk in their sin, is not what Jesus did. He went to them, He helped them, He taught them, but He did not make himself intimately familiar with unbelievers, as you can see in the Gospels where His traveling companions were very small in number and specific persons He had selected.
The things Jesus did were an example for us, showing that those He spent intimate and resting time with were those who were the children of faith. If Jesus had spent that intimate, familiar time with unbelievers and the wicked, what example would that have set? It would have provided evidence to others that the sinful things of the world are accepted with God, and that's not the case; which means that in order not to take the name of our Lord in vain, which is about ambassadorship, meaning that we, being the children of God, represent the Lord Jesus Christ, our closest friends and colleagues should be in the church, and not by force, but it should be a desire to draw close to those who are of Christ. (i.e. If those who are of Christ have no desire for closeness with others in the faith, and/or avoid that, they should have a serious look into their hearts and judge themselves in righteous judgment.)
That's why I expanded our church online to those around the country and around the world via Skype, and why I even started this forum, was to give Christians who had been scattered an opportunity to not be alone if they had sanctified themselves in fellowship. However, this is still a problem that needs to be addressed, and it may be somewhat my fault for not explaining it well enough in teachings, putting emphasis on the importance of how we are exhorted among one another, and the example we set for the world to see.
The bottom line is that if we, who are born again in Christ, have intimate fellowship and keep close company with those who are not born again in Christ, it gives them the impression that they are accepted with God. That's dangerous because that is having an negative effect on their understanding for salvation, and thus, when we do not, by our actions of sanctification, separate ourselves from the things of this world, and those who are set on loving the things of this world, then we give unbelievers the impression that what they say and do is accepted with God the Father.
Love not the world, neither the things that are in the world. If any man love the world, the love of the Father is not in him.
-1Jo 2:15
So in order for us to be living in charity, we should be thinking on the things of others rather than on ourselves, which is the fulfillment of the law and prophets.
Look not every man on his own things, but every man also on the things of others.
-Phl 2:4
So if we are loving our neighbor as ourselves, then to have religious assembly only with those who are of Christ, and to have intimate fellowship (i.e. friendship) with those who are of Christ, then we love our neighbor as ourselves, showing our neighbors that, if they do not come to repentance, there is a separation between us and them, as Jesus will separate the goats from the sheep on the Day of Judgment.
When the Son of man shall come in his glory, and all the holy angels with him, then shall he sit upon the throne of his glory: And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats: And he shall set the sheep on his right hand, but the goats on the left... And these shall go away into everlasting punishment: but the righteous into life eternal.
-Mat 25:31-46
This is going to happen to them if they do not come to repentance (i.e. grief and godly sorrow) of wrongdoing and faith in Christ. There is no avoiding this. Therefore, we need to make them aware of it, and one of the ways we do that is by assembling together with the saints, choosing to be intimate with those who we will spend eternity with.
I am aware that this is still a major problem even in our own church, that there are still quite a number who do not care about this very much. For that, I take some of the responsibility that I have not taught these things as thoroughly as I should have. I have so many things that need to be done, and this is just one more thing that I have on my "to-do" list.