Theravada and Mahayana are like yin and yang in some ways.
Where one says, “No,” the other says, “Yes,” where one says… I don’t know, that’s all I’ve got, but you get the point. But the two aren’t really antagonistic or incompatible. In fact, they’re directly related. Not because they both consider Siddhartha Gautama to be a Buddha, but because they directly flow into each other without a distinct boundary between them.
That’s because there’s a nifty secret about the Noble Eightfold Path. Well, it’s not really a secret, it’s just something that we tend to overlook. This tiny little tidbit is the bridge between Theravada and Mahayana. The Eightfold Path isn’t just a list of dos and don’ts; it isn’t just a guide on how to think, speak, act, and concentrate.
The Path is segmented into two different levels (but not truly segmented), usually called the mundane and the supra-mundane. In non-highbrow-elbow-patch-scholar lingo, that’d be “ordinary” and “extraordinary” or “pragmatic” and “mystical.” The ordinary level consists of skillful means: words and suggestions, theories and practices, and the list of dos and don’ts. These are helpful, “Fingers pointing at the moon,” that assist in evening out the mind.
The mystical level is the place, the mind, that generates and develops those words and suggestions, theories and practices, and dos and don’ts. It’s not really a place; it just seems like one.
The things generated by that clear, compassionate, meditative mind are all skillful means designed to bring us back to that mind—like breadcrumbs or a lifesaver.
The pragmatic level is like a tree; the mystical level is like the ground. We don’t have to learn about the ground in order to benefit from the fruits of practice, but we have to learn a little bit about it if we want to start planting trees with the seeds we find in the fruit.
It’s natural to be curious about the seeds and have the urge to plant them somewhere. Each time I eat an apple, I want to turn into Johnny Appleseed.
The mind that the mystical level of the Path addresses is the very thing that Mahayana Buddhism is all about. Immediately after getting up from the Bodhi Tree, Buddha realized that he couldn’t transmit this mind directly; he had to find a way to help people find it themselves. That way was the Pali Canon and, eventually, the Mahayana Sutras as well.
The Theravada Suttas are about the tree and the fruits, how to care for the tree and how to crack open the fruit. The Mahayana Sutras are horticultural guides about the ground and the seeds.
This might all sound like a ploy by later East Asian schools to gain legitimacy, but it’s actually all right there in the Pali Canon. Pretty neat, eh? I think so anyway.
So Theravada and Mahayana are inextricably connected. When a Theravadin practitioner touches on that Mind Ground, on the supra mundane—when transmission occurs—they’ve started practicing Zen; they’ve entered the Mahayana. When a Mahayanist gives practical advice to people, they’ve touched on Theravada.
I think it’s important to realize this, that Buddhism is in fact a whole, a single inter-connected Path that began with Siddhartha and continued to develop over the millennia. As long as new additions or new slants on old teachings and methods stay true to the message, I think they’re great. It’s just evolution.