The paradox that we all wrestle with is how love has to get "dirty" to be love, how Jesus's vision of holiness involves embracing tax-collectors, sinners and prostitutes.
And yet, there's this impulse in some sectors of Christianity to keep our love "pure." We see this impulse at work in the mantra "hate the sin but love the sinner." The idea here is that we can, with surgical precision, make a cut between our affections toward human persons and how we feel about their behaviors. But as I argue in Unclean, such surgical precision is psychologically untenable. And we know this. It is incredibility hard to not let a person's behaviors affect how we feel about him or her.
So when we come to embrace human beings our strong feelings about their behavior do get marginalized. And to those looking on that embrace looks like we are getting "soft on sin." And here's the provocative claim of Unclean: That's true. When you embrace sinners there is a sense in which you are pushing their sin to the background. That is, when you love sinners there is a sense where you are looking at the person first. Sin has been removed as the perceptual filter, as the central focal point. And that perceptual shift, moving the human being into the foreground and the sin to the background, has a psychological feel, an emotional tone that could be labeled "going soft on sin." Sin has been perceptually de-centered--so that the human person can stand in front of you--and has become less emotionally charged. A perceptual and emotional rearrangement has occurred.
My point in all this is that it's really hard to keep love pure. When you love sinners--and I mean really love them, as in affectionately and not just verbally and theologically--a sort of contamination is involved. Things get a bit blurry and messy in your heart. That's why we say things like "love has to get dirty."
I was recently reminded of all this reading a quote from Dietrich Bonhoeffer from his Ethics:
Just as God's love entered the world, thereby submitting to the misunderstanding and ambiguity that characterize everything worldly, so also Christian love does not exist anywhere but in the worldly, in an infinite variety of concrete worldly action, and subject to misunderstanding and condemnation. Every attempt to portray a Christianity of "pure" love purged of worldly "impurities" is a false purism and perfectionism that scorns God's becoming human and falls prey to the fate of all ideologies. God was not too pure to enter the world.