See, Paul's point (and he totally has one) is that we're all kind of like kids who are about to inherit a fortune. Hear him out.
Basically, Daddy Warbucks has left us a pile of money and a slew of European hotels, but until we turn 18, we can't get our hands on any of it.
Same thing with God. He promised that we'd be redeemed if we believed in him, but we couldn't actually do it until Jesus came to Earth.
Now we can claim our birthright as children of God. And start playing the stock market, too.
Now that the Galatians know God so intimately and have been adopted as his super special children, why would they want to go back to those dark days being forced to obey the law?
Paul is worried that the Galatians just aren't getting it. They're spending a lot of time fussing over which Jewish holidays to celebrate instead of just living for Jesus like they're supposed to.
Look, Paul knows that the Galatians have good hearts.
When he first came to see them, he was pretty darn sick. But they didn't hate on him because of it. They welcomed him and accepted what he had to say.
So what happened to those good times, Galatians? Paul remembers when these guys would have given him the shirts off their backs or the eyes out of their eye sockets. Um, gross.
Now they think he's just a big liar?
The Galatians are like Paul's kids. In fact, right now he's like a mom going through labor pains with them. And you know birthing a whole community of Christians is no picnic.
If the Galatians love the Torah so much, maybe they'd like to hear a story from the Torah. Yeah, Paul thought they would.
Remember Abraham and his two sons, Ishmael and Isaac?
Hagar was the mother of Ishmael. She was a slave woman whose son came into the world in the usual way (i.e., sex). Boring, right?
But Sarah, the mother of Isaac, was infertile, and God himself allowed her conceive a child. Isaac, therefore, came into the world through God's promise.
Paul thinks that the two women represent two different paths.
Hagar was a slave and bore children who would become slaves (to the law).
But Sarah was free and she gave birth because of God's goodness and love. In case you didn't realize it, Sarah is the lady Christians should be aiming to emulate.
Paul also drops a hint of what should happen to these naysayers in Galatia who keep pushing the law. The community should follow the example of Abraham and throw Hagar and her law-loving children out into the desert.