Some people are put off by Paul's language of adoption because it's gender insensitive. They argue, "Wouldn't it be better to say that we become sons and daughters of God?" It would, but that misses the whole point. Some time ago, a woman helped me understand this. She was raised in a non-Western family from a very traditional culture. There was only one son in the family, and it was understood in her culture that he would receive most of the family's provisions and honor. In essence, they said, "He's the son; you're just a girl." That's just the way it was.
One day she was studying a passage on adoption in Paul's writings. She suddenly realized that the apostle was making a revolutionary claim. Paul lived in a traditional culture just like she did. He was living in a place where daughters were second-class citizens. When Paul said—out of his own traditional culture—that we are all sons in Christ, he was saying that there are no second-class citizens in God's family. When you give your life to Christ and become a Christian, you receive all the benefits a son enjoys in a traditional culture. As a white male, I've never been excluded like that. As a result, I didn't see the sweetness of this welcome. I didn't recognize all the beauty of God's subversive and revolutionary promise that raises us to the highest honor by adopting us as his sons.
Our adoption means we are loved like Christ is loved. We are honored like he is honored—every one of us—no matter what. Your circumstances cannot hinder or threaten that promise. In fact, your bad circumstances will only help you understand and even claim the beauty of that promise. The more you live out who you are in Christ, the more you become like him in actuality. Paul is not promising you better life circumstances; he is promising you a far better life. He's promising you a life of greatness. He is promising you a life of joy. He's promising you a life of humility. He's promising you a life of nobility. He's promising you a life that goes on forever.
Tim Keller, in his sermon "The Christian's Happiness," PreachingToday.com