What is Understanding?
When someone tells you a rule, that's knowledge. The sky is blue. I know this. But what can I do with this information? Not much.
When you have to figure out why the sky is blue, suddenly you're learning about light and refraction and atmosphere, and you have a greater understanding of the world around you that not only applies to colour but allows you to make reasonable guesses about why shadows behave differently at different times of the day and why we're not burned alive by the sun.
An understanding of language is not much different. When you figure out that to talk about something that's over and done with you stick an -ed on the end, you can apply that immediately to every situation you encounter. As you get deeper into the english language, you'll realize that the kind of nuance between 'I was tired' and 'I had become tired' can only be fully appreciated if you understand the purpose of the structure 'had become'. Aah, had implies some sort of later action, which likely means stopping being tired. Clarity.
Not having rules to follow is a bit scary. But this is good for some people. If you understand a thing, you're directly connecting it with the part of the brain you're going to use later to produce it. Thus the steps between figuring out how to talk about yesterday and actually talking about yesterday are minimized. Your brain already knows how to pattern-apply, you're just giving it a different set of patterns. It pretty much does the rest without you.
Of course, understanding's only the beginning. You've still got to use the pattern. Tell your brain where to find it when it needs it. But that's the easy part. No, I lie. When you change the way you look at language, they're all easy parts.
The cards are as close to immersion learning as I think it's possible to get without actually moving to a foreign country.