One day Jesus said some words that were revolutionary to His hearers: "This, then, is how you should pray: 'Our Father in heaven...'"
Never before had anyone dared to call God "Father" — not in a personal sense.
Today, we've lost the revolution. Christians and even non-Christians easily believe that God is their father and, more importantly, they are His children — even when it's not true.
Some even dare to call "all God's creatures (i.e., animals and plants)" His "children." They're not.
We're all God's creations, yes. Whether directly or indirectly, God has a hand in the creation of every living thing. That doesn't make us His children.
If I make a chair, it's not my child. My daughter and I are building a robot dog; it's not my child either. If I could create a bacteria out of chemicals in a lab, it wouldn't be my child. Even if I could cobble together a human being out of spare parts, that being would not be my child.
My child is the one I begat, not made.
Or, if we successfuly adopt, my child will be the one we choose to adopt.
God has chosen to adopt some humans. Specifically, He's chosen to adopt those who place their trust in the death and resurrection of Jesus for the forgiveness of their sins. "[T]o those who believed in his name, he gave the right to become children of God."
God didn't have to save us. We're all rebellious sinners, desperately wicked. Once He rescued us from that, He had every right to view us as pets, slaves, servants, or (if He was feeling really generous) friends. But He chose to go one step farther, adopting us into His family, naming us "heirs of God and co-heirs with Christ."
Stop today and marvel at the gift we've been given. Wonder anew with the apostle, "How great is the love the Father has lavished on us, that we should be called children of God!"