In his writing Costly Grace, Dietrich Bonhoeffer talks about Christians receiving the grace of God with out repenting. Cheap grace is believing that your sins are paid for, but you have no need to live differently from the rest of the world. Bonhoeffer says "That is what we mean by cheap grace, the grace which amounts to the justification of sin without the justification of the repentant sinner who departs from sin and from whom sin departs." Costly grace is receiving the grace of god and fighting against the desire to live a life that is acceptable to the rest of the world. The avatar must also fight this desire. He is faced with the challenge of defeating the Fire lord, but to do this requires violence; exactly what the avatar is trying to prevent. The rest of the world and even the past avatars are telling him to kill, but that would be the cheap grace. He instead looks for the right way to end it, the way the avatar should live his life. Aang is not choosing the easy route of cheap grace, he is repenting and accepting his complete role as the avatar without submitting to worldly standards.
