And then I became a parent and it made a lot more sense.
But there's something else, too. A parent's role is different that a grandparent's. A child's main care, upbringing and provision should come from his parents. A grandparent should be able to supplement nurturing while still being able to fawn over and spoil a child in a way that parents cannot. The love of a grandparent differs from that of a parent perhaps not in degree but in kind.
I'm really not trying to make a point about family dynamics as much as I am about relationships with God. God does not want to be removed from us in a way that keeps Him out of major (or even minor) decisions. Parents name their children, decide which bedroom is theirs, and are responsible for the majority of disciplinary decisions.
Now when I think about God not having grandchildren I think about closeness. And not just the sweet-cuddly kind. The wake-up-with-you-in-the-middle-of-the-night kind. The pay-for-your-braces kind, The take-care-of-you when-you're-sick kind. The I-love-you-too-much-to-allow-that-behavior kind. He wants to be The Source. Not a resource.
I'm not saying that being a grandparent is a worry-free sunshine and lollipops walk in the park, and I know that lots of grandparents have stepped into a role of raising their grandchildren. My opinion about the love of a grandparent has not changed. My boys' grandparents love them so fiercely there's no way it doesn't reflect the love of God and I can't tell you how thankful I am for them.
What I am saying is that God wants all of us. He wants to be the one signing our permission slips and helping us with our homework every night. But unlike earthly parents He doesn't get tired and His patience is infinitely stronger. That's why He's God the Father. He wants you in His house under His specific care. He doesn't want you to be His kid's kid. He wants you for His own.
P.S. If you're interested in more of this topic,here.
Ken Ham has already expanded on it