The mystery of man and woman in marriage is, according to St Paul, something to think about in regard to the relationship between Christ and the church. Now I have a few people with whom I'm doing "pre-marriage counseling", which for the most part consists of coffee and conversation.
There are two thoughts which I find important, perhaps the most important, to share. First, I find it is often the case with young people of faith that they hope that by being married, they can (insert your terms here) do more of God's work; that they can, as a couple be of more use to the kingdom, than if they remain single. That is, they see the marriage as a means to another end, albeit a noble means and a noble end. What I try to get across is that I think the marriage itself is the witness, the further work, by which God will speak to their world.
The second point is this: in taking a marriage vow you are essentially committing yourself to an unknown. You are committing yourself not to who the person is (that is usually the enticement to marriage), but rather you are committing yourself to whomever the person will become. And that is to commit yourself to an unknown.
Now what has this to do with Christ and the church? Well, is it not possible to commit oneself while recognizing at the same time that we are committing, joining ourselves, to an "unknown"? This works two ways. Of course we can say that we know something of God, of Jesus. But we also sign on to who he will reveal himself to be more fully, and that is the unknown. On our side, I think we also must learn that when we enter this faith, we ourselves are committing to become whatever he wishes us to be - which again is an unknown. Paul once tried to persuade us that if anyone is in Christ, that person is a new creation. Not merely a renovation of the old one, but a new creation. We (or at least I) generally tend to go for the renovation idea - redemption is not really about "new creation"; it is more about transforming who I already am, with all the things which I believe contribute to my identity. But what would it be like if the offer really was to be a "new creation" - something entirely new born out of the imagination of God? I think that is the possibility to which we submit ourselves when we truly desire to be "in Christ". We commit ourselves to becoming something we have not yet even imagined.