I'm still struggling with the concept of good karma, bad karma, and both good and bad karma. If all actions are one of the above- and, as I understand it, mostly the latter, it seems as if we will always be generating bad karma. Is following the 8-fold path going to insure only creating good karma or will we still be generating both as we struggle on the path?
I think its helpful to bear in mind the different between Karma and it's fruit (or vipāka). An action may have a karmic effect if it has ethical or volitional weight but it's fruit doesn't occur immediately. It might occur years later, in another life or it might fizzle out before it ever occurs.
The relevance of this is that a person might generate a whole lot of 'bad' Karma but this karma might only bear fruit well after the person has undergone a tremendous amount of spiritual progress. So 'bad' Karma storing up to bear fruit won't stop them on the spiritual path. They might however have to deal with the effects of that bad action when they are an entirely different sort of person.
A good example of this (from the Pali Canon so this has a Therevadan focus now) is the story of Angulimala. He was a notorious bandit and murderer who encountered the Buddha and then became the Buddhas disciple. His 'bad' Karma didn't stop him ultimately becoming a ahrant. However he still had to deal with the fruits of his bad conduct well after his conversion. At one point his was seriously attacked by resentful villagers while on his alms round. Even though he was no longer a murderer he still had to deal with the consequences of his 'bad' Karma.
So just to summarise, your previous bad Karma won't necessarily stop your progress on the spiritual path. But it's likely that you will at some point have to deal with the fruits no matter how spiritually adept you may become.
The process of creating Karma will only stop when you are liberated.
In the mean time what you can do is:
- Do good Karma
- Reduce bad Karma as much as possible
With regard to reducing bad Karma is the be mindful and equanimous with respect to all sensations you experience. If you look at Dependent Origination, there is a link between feeling (sensation) and craving. So once you get a pleasant, unpleasant or neutral feeling you have to be equanimous with the knowledge that it is impermanent. Then momentarily craving does not arise. When you manage to do this continuously you are not generating any new Karma. Then all you old stock of Karma will start manifesting themselves as pleasant, neutral and unpleasant sensations and pass away once they have given result as a sensation. Once you maintain equanimity and all your Karma that can lead to rebirth in lower realms has passed away you will experience a dip into sainthood.
When all the seeds of bad karma giving rebirth in lower realms have are passed away you are not creating any new Karma taking you to lower realms, you mind is ready to take the 1st dip into the 1st stage of Sainthood as interpreted by Ledi Sayadaw linage.