"Cheap grace is grace without the cross, grace without the living, incarnate Jesus Christ. Costly grace is the gospel. It costs people their lives. It cost the life of God's Son, and nothing can be cheap to us which is costly to God." - Dietrich Bonhoeffer in Discipleship
When we take sin lightly, we fail to recognize the weight of the cross and the measure of God's love for us. We think that our salvation came free because we don't have to pay the price. But freedom is never free. The cross is where we find love in its truest form. And I can stand secure because I know that I am beloved of God. It was His pleasure to crush His Son that I would find eternal life and forgiveness.
Instead of thinking about a cause worth dying for, what are you are you willing to live for? That is the question that the people of God must consider. Most of us won't be asked to die a physical death for our faith. But we are all called to live a sacrificial life of love focused on God and His kingdom.