In Nadia Bolz-Weber’s sermon on Reformation Sunday (or “Lutheran Pridefulness Sunday” as she likes to call it) she articulates how to tell the difference between Law & Gospel.
“You can tell the Law because it is almost always and if-then proposition – If you follow all the rules in the Bible God then will love you and you will be happy. If you lose 20 pounds then you will be worthy to be loved. If you live a perfectly righteous Green eco lifestyle then you will be worthy of taking up space in the planet. If you never have a racist or sexist or homophobic thought then you will be worthy of calling other people out on their racism and sexism and homophobia. The Law is always conditional and it is never anything anyone can do perfectly. When we treat Law as Gospel there can never be life and happiness and worthiness. Under the Law there are only 2 options: pride and despair. When fulfilling the ‘shoulds’ is the only thing that determines our worthiness we are either prideful about our ability to follow the rules compared to others or we despair at our inability to perfectly do anything. Either way, it’s still bondage”
It’s important to know the distinction because churches confuse the two.
To read and hear her whole sermon check out her blog.