Some of the objectives for this rover to complete were...
1.) Characterize the mineralogy and textures of rocks and soils and determine the processes that created them.
2.) Search for geological clues to the environmental conditions that existed when liquid water was present.
3.) Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites.
4.) Search for and characterize a variety of rocks and soils that hold clues to past water activity.
So, mainly, this rover was made to study rocks and soil on the surface of mars. Spirit was set on the opposite side of Mars that Opportunity was set on.