How did Mendels use of purebred plants contribute to his understanding of inheritance?

As found on the Wikipedia page on Gregor Mendel:

"This study [Mendel's pea plant experiments where he crossbred two pea plants, one purple and one white and from there it demonstrated dominant and recessive alleles] showed that one in four pea plants had purebred recessive alleles [usually white], two out of four were hybrid and one out of four were purebred dominant. His experiments led him to make two generalizations, the Law of Segregation and the Law of Independent Assortment, which later became known as Mendel's Laws of Inheritance."

Breeding two of the pure, purple plants would yield only pure purple plants, however the hybrid ones (which would look like the pure ones) would yield three purple looking ones (one was pure, the others had recessive alleles) and the last one would be white (all recessive alleles) thus Mendel was eventually able to see that recessive alleles didn't just crop up randomly, they were traits that were suppressed and passed on invisibly to the next generation of plants. (sorry for the length >.< I hope this was helpful)