Grace is not free.
The Christian concept of grace (charis, Χάρις) has puzzled me for years. Its definition seems a good place to begin. Still, I hate to start with a definition, so I’ll start with a story.
During a British conference on comparative religions, the participants were heatedly discussing what’s unique about Christianity. C. S. Lewis wandered into the room. “What’s the rumpus about?” he asked, and heard in reply that his colleagues were discussing Christianity’s unique contribution among world religions. Lewis responded, “Oh, that’s easy. It’s grace.” (Yancy, p 45) *
It’s a good point, but not strictly true. Hindus and Muslims believe in Grace, understood as God reaching out to humanity with love. Jews believe in chen (חֵן), a version of grace. Nevertheless, it is Christianity that has developed the concept most fully.
The standard definition
In Christianity, grace is the love and mercy given to us by God as a free gift. It is nothing we have earned.
Grace is favor, the free and undeserved help that God gives us to respond to his call to become . . . partakers of the divine nature and of eternal life. (Catechism of the Catholic Church)
This definition leads some to see grace as part of a faith over works teaching. It leads others to think that if grace is free then it must be easy. Both conclusions are wrong. Dietrich Bonhoeffer calls this “cheap grace.”