The Path of Light was a front by the Eighth Son used to make inroads with the peasants of Stin Cepel.
During the famine caused by the chaos in the Faewild during Episode III: Awakening, the Eighth Son sent agents to Stin Cepel to hand out free food to the peasants. His goal was to slowly push eastward toward the capital, and then convince the people that their Queen had abandoned them.
This plan failed, however, when the Sandstriders figured out the true nature of the movement and warned the Queen. Her military disbanded the Path of Light.