This Momentary Marriage: A Parable of Permanence by John Piper. You can download the book as a free PDF file.
"Marriage exists to display the covenant-keeping love of Christ and His church."
Once you understand that statement, you can understand why marriage doesn't exist in heaven-- when Christ and His church are together. You can understand why husbands and wives have different roles (Eph. 5), the husband representing Christ, and the wife representing His church, so it's important not to get the roles confused. You can understand why divorce is sin-- Christ would never abandon His church. And you can understand why the purpose of marriage isn't to make children.
Every chapter is introduced with a quote from Bonhoeffer, this sets a great tone on the un-permanence of marriage. It also deals with singleness and childless marriages-- both are perfectly fine-- so it's useful to read no matter your status.
My wife and I decided to read through this book together as a study, and that's been good. Piper gives a great biblical defense of everything he writes. His books are always God-exalting, and this is no different. He gives you a great appreciation for God's plan for marriage from Genesis to Revelation.
It's a pretty quick read, too. I give it 4 stars out of 5.