More from Ajahn Thanissaro on understanding how karma and the divine mind states work together:
A third lesson from the principle of karma is that developing the brahma-viharas [sublime mental states] can also help mitigate the results of your past bad actions. The Buddha explains this point with an analogy: If you put a lump of salt into a glass of water, you can’t drink the water in the glass. But if you put that lump of salt into a river, you could then drink the water in the river, because the river contains so much more water than salt. When you develop the four brahma-viharas, your mind is like the river. The skillful karma of developing these attitudes in the present is so expansive that whatever results of past bad actions may arise, you hardly notice them.
A proper understanding of karma also helps to correct the false idea that if people are suffering they deserve to suffer, so you might as well just leave them alone. When you catch yourself thinking in those terms, you have to keep four principles in mind.
First, remember that when you look at people, you can’t see all the karmic seeds from their past actions. They may be experiencing the results of past bad actions, but you don’t know when those seeds will stop sprouting. Also, you have no idea what other seeds, whatever wonderful latent potentials, will sprout in their place.
There’s a saying in some Buddhist circles that if you want to see a person’s past actions, you look at his present condition; if you want to see his future condition, you look at his present actions. This principle, however, is based on a basic misperception: that we each have a single karmic account, and what we see in the present is the current running balance in each person’s account. Actually, no one’s karmic history is a single account. It’s composed of the many different seeds planted in many places through the many different actions we’ve done in the past, each seed maturing at its own rate. Some of these seeds have already sprouted and disappeared; some are sprouting now; some will sprout in the future. This means that a person’s present condition reflects only a small portion of his or her past actions. As for the other seeds, you can’t see them at all.
This reflection helps you when developing compassion, for it reminds you that you never know when the possibility to help somebody can have an effect. The seeds of the other person’s past bad actions may be flowering right now, but they could die at any time. You may happen to be the person who’s there to help when that person is ready to receive help.
Karma is a widely misunderstood concept in Buddhism. It includes, but is not limited to, the idea of “plant a radish, get a radish”. There are different intensities of intention, results that are short-lived or long-lived, changes of heart that can ease prior hurts, so many variations that the Buddha said if you try to understand it all, your head might explode. It’s important to be humble when thinking or speaking of karma. The most important use of the idea is this: What we do now is our only opportunity to make a positive difference, for ourselves and anyone else. What’s in our hearts now?