Who is a tzaddik or tzaddeikit? Who are the righteous of the world? R. Zalman Schachter Shalomi, in A Heart Afire writes: "Are they not those who are participating in righteousness at that moment? That is what we are talking about here, the will directed toward righteousness in any given moment. Those who participate in that "aggregate will" are the tzaddikim for whom G-d created the world."
It's interesting that the root of tzaddik (righteous person) is tz-d-k, which also forms tzedek (justice) and tzedekah (translated as charity but really means more the justice that comes from sharing the material wealth of which we are only... stewards). Therefore, I like to think of tzaddikim as justice-ers, people working to bring justice to the world.
Extending the thinking that G-D created the world for tzaddikim, we could conclude that G-d created the world on purpose as a place intended for social action and that humans are intended to work for justice: "Tzedek, tzedek, tirdof" ("justice, justice shalt thou pursue." Shoftim (Deuteronomy) 16:20). That pasuk goes on to imply that justice is what is necessary, it is in fact a prerequisite, for us to thrive and come into our inheritance (that is, the world in which we live).