The basic claim I want to make: Holiness is a means toward an end, not an end in itself. Holiness is a bit of missional equipment, a missional tool. What sort of tool?
I take my cue here from Jesus, how he frames the relationship between holiness and mission in his High Priestly Prayer in John:
My prayer is not that you take them out of the world but that you protect them from the evil one. They are not of the world, even as I am not of it. Sanctify them by the truth; your word is truth. As you sent me into the world, I have sent them into the world. For them I sanctify myself, that they too may be truly sanctified (John 17.15-19. emphasis added).
The language of holiness -- "sanctify" -- and mission --"sent" -- intermingle in the text. Jesus prays for his disciples to be sanctified -- to be set apart, to be holy. But why? As an end in itself? No, as a means to an end, a missional end, being sent out into the world.
More specifically, holiness is revealed to be a form of protection that equips us to be missional people. In this, holiness doesn't take us out of the world but is the means by which be become radically available to the world.
Let me give a concrete example of what I'm talking about.
Let's talk about sex.
Why should we pursue sexual purity? Why should we be holy when it comes to sex?
The answer that we have tended to hear is that sexual purity is "what God wants". (This is, sadly enough, the constant refrain on the sad show, Preacher's Daughters. It's sad, because it's not enough -- it misses the boat on all that the NT has to say about such things. But that's for another day.) Consequently, the pursuit of sexual purity becomes an end in itself (as in the most recent episode of Preacher's Daughters). But what I'm suggesting is that sexual purity should, rather, be seen as a means to a missional end. Specifically, sexual purity is a form of protection that allows you to be radically available to others.
Let me describe what this looks like from my social location as an engaged man who's also a minister. How can I be radically available to others -- women in particular -- if I'm not sexually pure, if I'm not holy? Pushing further, let's say God is sending me into very dark places in the world, sexually speaking. Let's say I find myself ministering to sex workers, women in the adult entertainment industry or with women caught up in sex trafficking. How can I be in the midst of these very dark sexual places if I'm not holy?
And the examples don't have to be dramatic. How can I be radically available to these people in my life, an agent of grace, if I'm not sexually holy? Think of examples from your own social location.
I hope all this illustrates why I call holiness a form of protection. Holiness is a form of moral protection that equips us to be missional people, a people radically available to the brokenness of the world. Holiness is apostolic in nature, the equipment needed for those sent into the world as God's emissaries of love and grace.
Tick through other examples beyond sexuality. Think of other "sins" and how each compromises your ability to be radically available to others in particular situations. Money and power are other obvious examples. (This would be why the Bible highlights kindness and humility as forms of holiness.)
In short, holiness isn't a separation from the world. Holiness is what allows us to be radically in and available to the world.
Just as Jesus was radically in and available to the world.