Kimchi is a Korean fermented pickle. Pickling is an ancient way of preserving food, but it also creates new flavours in the process. Modern pickling relies on vinegar to produce an acidic solution that preserves food. In the old days before you could just head to the store and buy buckets of vinegar, you had to find a way to create an acidic solution from scratch. Kimchi belongs to the latter class of pickling. Essentially, you douse your vegetable with salt to keep most of the food-spoiling nasties at bay, and then let lactic acid bacteria kick into gear (they can take the salt, it seems) so they can produce the food preserving acids for you. The brine that swirls around in this pickling soup adds all kinds of nice flavours to the finished dish.
Kimchi rocks! Peace. Out.