Why did God make all plants, but only some animals, kosher? Sources, please.
The famous saying "you are what you eat" may explain this. Plants do not tend to have any unruly behavior. However there are many animals that kill other animals and behave - in lack for a better term - animalistic. Hashem does not want us to eat from these animals, in order that it should not make us behave in the way they behave.