What is the significance of "Purim Katan"?

In a leap year such as this year, there are two Hebrew months of Adar.
Marriages, births and deaths that took place in Adar of a non-leap year are all celebrated in the second Adar. The holiday of Purim, too, is celebrated in Adar II on the 14th of the month. However, it is customary to recognize the 14th of Adar I as "Purim Katan," or the Minor Purim.
This is done by making meals of a festive nature, not delivering eulogies and not fasting.