Some Christian students earlier this week were sharing that they were concerned about their Christian friends going out with non-Christians. One said her friend was justifying it because 'she spoke of Jesus to him the whole time'.
My principle concern with this is not that they're going out with non-Christians. That is the symptom. They think, "I won't drift: I'm strong in my faith." But that's still not the ultimate concern (though it probably will happen): that's a symptom. The principle concern is that they are treasuring being in a relationship, or this relationship, or this man, more than they treasure Christ. That is my main concern. That is the root issue.
Why do I say that? Surely knowing God's love means that we overflow with more love for others, indiscriminately, as his? This is true. But if we treasure Christ supremely we will not be joined to one who considers him a liar ("a good man"), a fraud ("a revolutionary") or a lunatic ("sincerely misguided"). If we consider that Jesus is Lord, we will not become one with one who considers themselves to be lord. If we are a new creature in Christ, with the Spirit of life dwelling in us, we will not unite with a stinking corpse. If we are reconciled to God in Christ, we will not join with one who's a slave to the enemy. So I say, my principle concern is that they treasure the relationship or the man over Christ, who is infinitely precious and gloriously sufficient.
So the problem is idolatry: putting a right desire (that for relationship, marriage, etc) in the controlling place of the heart, where only Christ should reign.
So how to respond? To merely say, "But you shouldn't go out with a non-Christian: you'll drift" falls far short of addressing the problem. The heart issue is idolatry, and it's probably exposed like this: how do they justify going out with said non-Christian? 90% of the time, the answer will somehow express that "It'll work out". The relationship will be a success. "We love each other; he respects my faith." In other words, their ultimate aim is a sucessful middle-class marriage. That's the idol. Since when did God tell us his plan for us was a happy middle-class marriage??
Another response which may come is this, "I go on to him all the time about Jesus: and I did say I wouldn't go out with him unless he comes to church with me, and he does." But it doesn't matter tuppence if the girl goes on to him incessantly about Christ with her words: meanwhile, she is proclaiming with every inch of her being that he / the relationship is more important than Christ. More precious. More desirable. More fulfilling. Supreme. He doesn't hear "Jesus is Lord" but "You are Lord - and Jesus is a nice optional extra."
So when a friend is going out with a non-Christian, or considering it, why not study the person and work of Christ for a while with your friend? Colossians, perhaps? Do some demolition work on the idols of the heart, and pray that the Holy Spirit, through His word, will build a proper altar in place of the idol-rubble: that of Christ and his finished work. Not going out with non-Christian won't do much good. Being filled with covenant love for Christ in response to his initiated love will change everything. And while you look together at God's word, don't despair for your friend but pray with this hope: a right passion has got in the wrong place (the controlling place) - but the Holy Spirit yearns jealously for Christ's Lordship to be restored there, and therefore will give more grace. (James 4)