Just start talking about Grace.
It's great. They get rather freaked out and start saying stuff about how, "You still have to do stuff and that doesn't mean you don't have to follow the law and yeah but we still have to do good works."
And then you're there like... "Um, yes, I never said otherwise."
I'm am pretty sure that we've gotten terribly confused. I know I was terribly confused. (probably will be again, too. But anyways.)
Grace is not like that at all. Grace doesn't mean, "Oh wonderful!! Now I can just sit around and do nothing (or whatever awful things I want to do.)" No, no, no.
Grace means Jesus dying on the cross. And then rising again.
Grace is given freely, because that is what kind of God there is.
Grace is very, very costly, because that is what kind of God there is.
By the first statement I made, "Grace is given freely, because that is what kind of God there is." I meant that He gives it freely because He is a gracious, loving God.
By the second statement, "Grace is very, very costly, because that is what kind of God there is.", I mean that God is holy and just, and cannot tolerate sin. He can't just gloss it over with a hug and say it'll be fine.
It took Jesus' perfect fulfillment of the law. It took His death, horrible in every sense of the word, on the cross. It took His rising again, His conquering of death.
Grace is given freely.
Grace is not free.
Grace enables us to learn to live as Christ lived. It gives us safety and confidence while we learn--we are not under the law, but under grace. We're still learning, we're still becoming like Christ, we're still doing good things.
But it's all different.
The motivation is different: It's our love for God, rather than our fear of the law. Over and over, Jesus says "If you love Me, obey my commandments."
The power is different: It is no longer our vain human efforts; now it is grace/the Holy Spirit that works in us.
The end result is different: Under the law, no matter how hard you tried, you would fall short. Always. Every. Single. Time. With grace, He makes the way, hits the target right on--for you. Because of His sinless life in YOUR place, because He took YOUR punishment, because He always lives to make intercession for YOU... you are accepted, holy, and beloved.
Grace, properly understood, won't make anyone stop working. No, it will motivate you all the more. Grace is amazing--a precious, priceless, undeserved, unearned gift.
A gift of love.
And because He first loved us, we, in turn, love Him. And through His grace, we become more and more like Him.