“…the Kingdom of Heaven is not a place, but a state of mind.”

Exiles (1915), Act II http://www.robotwisdom.com/jaj/exiles2.html

Chapter 11 The Textbook of Love http://www.unification.net/truelove/tl1-11.html 1984-02-05

Source: Heaven Revealed (Moody, 2011), p. 85

Lyra to Pan in Ch. 38 : The Botanic Garden
Source: His Dark Materials, The Amber Spyglass (2000)
Context: "I remember. He meant the Kingdom was over, the Kingdom of Heaven, it was all finished. We shouldn’t live as if it mattered more than this life in this world, because where we are is always the most important place."
"He said we had to build something…"
"That’s why we needed our full life, Pan... we wouldn’t have been able to build it. No one could if they put themselves first. We have to be all those difficult things like cheerful and kind and curious and patient, and we’ve got to study and think and work hard, all of us, in all our different worlds, and then we’ll build…"

Credo (1901)
Context: I believe in the Motherhood of God.
I believe in the Blessed Trinity of Father, Mother and Child.
I believe that God is here, and that we are as near Him now as ever we shall be.
I do not believe He started this world a-going and went away and left it to run by itself.
I believe in the sacredness of the human body, this transient dwelling place of a living soul, And so I deem it the duty of every man and every woman to keep his or her body beautiful through right thinking and right living.
I believe that the love of man for woman, and the love of woman for man is holy; And that this love in all its promptings is as much an emanation of the Divine Spirit as man's love for God, or the most daring hazards of the human mind.
I believe in salvation through economic, social, and spiritual freedom.
I believe John Ruskin, William Morris, Henry Thoreau, Walt Whitman, and Leo Tolstoy to be Prophets of God, who should rank in mental reach and spiritual insight with Elijah, Hosea, Ezekiel, and Isaiah.
I believe that men are inspired to-day as much as ever men were.
I believe we are now living in Eternity as much as ever we shall.
I believe that the best way to prepare for a Future Life is to be kind, live one day at a time, and do the work you can do best, doing it as well as you can.
I believe we should remember the Week-day, to keep it holy.
I believe there is no devil but fear.
I believe that no one can harm you but yourself.
I believe in my own divinity — and yours.
I believe that we are all sons of God, and it doth not yet appear what we shall be.
I believe the only way we can reach the Kingdom of Heaven is to have the Kingdom of Heaven in our hearts.
I believe in every man minding his own business.
I believe in sunshine, fresh air, friendship, calm sleep, beautiful thoughts.
I believe in the paradox of success through failure.
I believe in the purifying process of sorrow, and I believe that death is a manifestation of life.
I believe the Universe is planned for good.
I believe it is possible that I shall make other creeds, and change this one, or add to it, from time to time, as new light may come to me.

Source: The Great Divorce (1944–1945), Ch. 9

Source: Letters, p. 89

1920s, Process and Reality: An Essay in Cosmology (1929)

i.254-255
Paradise Lost (1667)
Variant: The mind is its own place, and in itself
Can make a heav'n of hell, a hell of heav'n.
Source: Paradise Lost: Books 1-2