Just to clarify about the oracles - while we use religious terms and 'preaching', technically the oracles are not a religious group, they dont believe in spirits or supernatural power, only enlightenment (aka knowledge/learning) and peace.
The oracles were 'taught' the truths of sirius by the shrine itself, which is left over from the daam k'vosh civilization. They have learned a great deal about nomads, the k'vosh, and sirius itself - from long before humans arrived. They use this knowledge as their foundation for 'converting' the humans of sirius into a more peaceful society. Primarily, they fight against concepts of greed, powermongering, and violence.