If you think legalism is simply too much emphasis on the law, then you will think the antidote is to talk less about obedience and more about acceptance and forgiveness. If you think that antinomianism is simply too loose an attitude toward morality and law, you will assume the remedy is to talk less about mercy and acceptance and more about God’s righteousness and holy commands. In short, you will try to cure one with a dose of the other. That will be a disaster, because both of them have the same root cause. Both come from the belief that God does not really love us or will our joy, and from a failure to see that “both the law and the gospel are expressions of God’s grace.” For both the legalist and the antinomian, obedience to the law is simply the way to get things from God, not a way to get God, not a way to resemble, know, delight, and love him for his sake.
Tim Keller, Preaching (pgs. 54-55).