Question

what was the purpose of hardy and weinberg's work?

Answer 1

Hardy and Weinberg proved mathematically that the allele frequencies between successive generations will not change, so long as the population is not subject to external evolutionary factors.

Basically, if evolution was allowed to occur within a population and the population had no ability to choose mates, be influenced by the environment, etc... then the alleles present in the population for each gene and the fraction of members in the population with certain alleles would remain constant from one generation to the next.

For the derivation of this probability argument, take a look at the wikipedia page. It actually lists all of the mathematical derivations.
http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle#Derivation_of_Hardy.27s_equations

Answer 2

The purpose, well ,really what it proves is what EVOLUTION IS NOT. You know the Hardy Weinberg equilibrium, is basically like the perfect population, no evolution basically. So it is a null hypothesis.