Writes pastor and author Timothy Keller in his new (and very good!) book The Meaning of Marriage (Dutton, 2011), pages 47–49:
So, what do you need to make marriage work?
You need to know the secret, the gospel, and how it gives you both the power and pattern for your marriage. On the one hand, the experience of marriage will unveil the beauty and depths of the gospel to you. It will drive you further into reliance on it. On the other hand, a greater understanding of the gospel will help you experience deeper and deeper union with each other as the years go on.
There, then, is the message of this book — that through marriage the mystery of the gospel is unveiled. Marriage is a major vehicle for the gospel’s remaking of your heart from the inside out and your life from the ground up.
The reason that marriage is so painful and yet wonderful is because it is a reflection of the gospel, which is painful and wonderful at once. The gospel is this: We are more sinful and flawed in ourselves than we ever dared believe, yet at the very same time we are more loved and accepted in Jesus Christ than we ever dared hope. This is the only kind of relationship that will really transform us.
Love without truth is sentimentality; it supports and affirms us but keeps us in denial about our flaws. Truth without love is harshness; it gives us information but in such a way that we cannot really hear it. God’s saving love in Christ, however, is marked by both radical truthfulness about who we are and yet also radical, unconditional commitment to us. The merciful commitment strengthens us to see the truth about ourselves and repent. The conviction and repentance moves us to cling to and rest in God’s mercy and grace.
The hard times of marriage drive us to experience more of this transforming love of God. But a good marriage will also be a place where we experience more of this kind of transforming love at a human level. The gospel can fill our hearts with God’s love so that you can handle it when your spouse fails to love you as he or she should. That frees us to see our spouse’s sins and flaws to the bottom — and speak of them — and yet still love and accept our spouse fully. And when, by the power of the gospel, our spouse experiences that same kind of truthful yet committed love, it enables our spouses to show us that same kind of transforming love when the time comes for it.
This is the great secret! Through the gospel, we get both the power and the pattern for the journey of marriage.