Friends beliefs are generally not codified. We have no creed. Some point to Friends Testimonies to describe Quaker beliefs. These are typically published by various Friends Organizations in what is called either a Faith in Practice or a Book of Discipline. Almost all these publications start with the following quote…
“Dearly beloved Friends, these things we do not lay upon you as a rule or form to walk by, but that all, with a measure of light which is pure and holy, may be guided: and so in the light walking and abiding, these things may be fulfilled in the Spirit, not in the letter; for the letter killeth, but the Spirit giveth life.”
Letter from Meeting of Elders at Balby, in Yorkshire, England, 1656
On the other hand, there is a concept in Quakerism that all Friends unite on. It is our heavy reliance on a direct and immediate Spiritual Experience. This can be traced back to the experience of the first Quaker, George Fox. As a young seeker, Fox was frustrated by the inability of the established Church to assist in his spiritual journey. His frustration grew to anguish before a pivotal event occurred. As he wrote in his Journal…
But as I had forsaken the priests, so I left the separate preachers also, and those esteemed the most experienced people; for I saw there was none among them all that could speak to my condition. When all my hopes in them and in all men were gone, so that I had nothing outwardly to help me, nor could I tell what to do, then, oh, then, I heard a voice which said, "There is one, even Christ Jesus, that can speak to thy condition"; and when I heard it, my heart did leap for joy.
Then the Lord let me see why there was none upon the earth that could speak to my condition, namely, that I might give Him all the glory. For all are concluded under sin, and shut up in unbelief, as I had been; that Jesus Christ might have the pre-eminence who enlightens, and gives grace, and faith, and power. Thus, when God doth work, who shall hinder it? and this I knew experimentally.
My desire after the Lord grew stronger, and zeal in the pure knowledge of God, and of Christ alone, without the help of any man, book, or writing. For though I read the Scriptures that spoke of Christ and of God, yet I knew Him not, but by revelation, as He who hath the key did open, and as the Father of Life drew me to His Son by His Spirit. Then the Lord gently led me along, and let me see His love, which was endless and eternal, surpassing all the knowledge that men have in the natural state, or can obtain from history or books; and that love let me see myself, as I was without Him.