"Inner Light" is a term Quakers use to describe the theological belief that God's presence resides inside every person. John 1:9 is a verse central to this doctrine:
"That was the true Light, which lighteth every man that cometh into the world." KJV
"The true light that gives light to every man was coming into the world." NIV
This doctrine was important as Quaker founder, George Fox, argued that Christians didn't need the Church to know God; they could just look inward. Quaker apologist, Robert Barclay, writes:
"This most certain doctrine being then received, that there is an evangelical and saving Light and grace in all, the universality of the love and mercy of God towards mankind, both in the death of his beloved Son the Lord Jesus Christ, and in the manifestation of the Light in the heart, is established and confirmed, against all the objections of such as deny it."
Quakers are encouraged to be attentive to their inner light and then share with others what they believe God revealed to them, particularly in the setting of corporate worship.