Yes it's a sin. It's of this world, which means it's of the flesh. Will He burn you for eternity for smoking it? No. But if you put it above Christ for your source of inner peace, and it becomes a habit, that's something to be concerned about. I'd say it's all right as long as you do it sparingly. Just know that there is a better high than any drug can ever give you. And it's fo' free.