A. Publicly Released Information
B. Generally Recognized Information
It was found in the White Moon with Adam at the South Pole. In essence, the Spear of Longinus is a security device that comes as a set with a Seed of Life.
C. Confidential Information
It is a spear which has a will and is a type of lifeform capable of moving by itself. This is an item close to a god and thus able to put a Seed of Life, who holds the power of eternal life, into suspended animation, and this is the reason why the Seed of Life does not reach god-status. The First Ancestral Race prepared this as a counter- measure in the event that a Seed of Life did not follow their own goals.
It is thought that a Spear acting as Lilith's counterpart was separated from it by the shock at the time of First Impact. This Spear has yet to be found. There is a chance that it may have been destroyed.
D. In-Depth Information
For the purpose of opening the Path to God, Gendo and Seele brought Lilith's growth to a point just before the final stage, and to temporarily delay this they are having NERV transport the Spear of Longinus that was paired with Adam.