Almaas, A.H., Essence. The Diamond Approach to Inner Realization, (Red Wheel Weiser: 1986).
Armstrong, Karen, A History of God. The 4000-Year Quest of Judaism, Christianity and Islam (Ballantine Books: New York, 1993).
Fields of Blood: Religion and the History of Violence (Alfred A. Knopf: 2014)
Aslan, Reza, Zealot. The Life and Times of Jesus of Nazareth (Random House: New York, 2013).
Besant, Annie, Esoteric Christianity (Theosophical Society: 1905; 2nd edition)
Easwaran, E., (transl), The Upanishads (Nilgiri Press: Tomales, California, 1987).
Eckhart, Meister, Eckhart: A Modern Translation, translated by Raymond B. Blakney (HarperTorch: 1986).
Selected Writings, translated by Oliver Davies (Penguin, 1994).
The Complete Mystical Works of Meister Eckhart, translated and edited by Maurice O’C Walshe (The Crossroads Publishing Company: New York, 2009).
Ehrman, Bart D., The Orthodox Corruption of Scripture. The Effect of Early Christological Controversies on the Text of the New Testament (Oxford University Press: New York, 1993).
Jesus. Apocalyptic Prophet of the New Millennium (Oxford University Press: 1999).
Lost Christianities: The Battles for Scripture and the Faiths We Never Knew (Oxford University Press: 2003).
Misquoting Jesus: The story behind who changed the Bible and why (HarperSanFrancisco: 2005).
The Lost Gospel of Judas Iscariot (Oxford University Press: 2006).
Peter, Paul and Mary Magdalene: The Followers of Jesus in History and Legend (Oxford University Press: 2008).
Jesus, Interrupted. Revealing the Hidden Contradictions in the Bible (and Why We Don’t Know About Them) (HarperCollins eBooks: 2009).
Forged: Writing in the Name of God – Why the Bible’s Authors Are Not Who We Think They Are (HarperCollins: 2011).
Did Jesus Exist? The Historical Argument for Jesus of Nazareth (HarperOne: 2012)
How Jesus Became God: The Exaltation of a Jewish Preacher from Galilee (HarperOne: 2014).
James, William, The Varieties of Religious Experience: A Study in Human Nature (Longmans, Green & Co: 1902).
Jung, C.G., Aion. Researches into the Phenomenology of the Self, translated by R.F.C. Hull (2nd edition; Princeton University Press: Princeton, 1968).
Answer to Job, translated by R.F.C. Hull (2nd edition; Princeton University Press: Princeton, 1969).
Levine, Amy-Jill, Dale C. Allison Jr and John Dominic Crossan (ed.), The Historical Jesus in Context (Princeton University Press: Princeton, 2006).
Miller, R.J. (ed), The Complete Gospels. Annotated Scholars Version (Revised and expanded edition; HarperSanFrancisco: San Francisco, 1994).
O’Reilly, Bill, and Martin Dugard, Killing Jesus. A History (Macmillan 2013).
Plotinus The Enneads as translated in W.R. Inge, The Philosophy of Plotinus (3rd Edition; Longmans, Green & Co: New York: 1929).
Robinson, James M. (ed), The Nag Hammadi Library (HarperCollins: 1981).
Schweitzer, Albert, The Quest of the Historical Jesus (1906). You can download it for free from www.gutenberg.org. There is also a free, very good talking book version at www.librivox.com.
St John of the Cross, The Collected Works of Saint John of the Cross, translated by Kieran Kavanaugh & Otilio Rodriguez (Revised edition; Institute of Carmelite Studies: Washington, 1991).
St Teresa Avila, The Interior Castle (Christian Classics Ethereal Library). Available for free at www.ccel.org. The section of the most interest is the last one, “The Seventh Mansions”.
Stace, W.T., (ed) The Teachings of the Mystics (Mentor Books: New York, 1960).
Steiner, Rudolf, Christianity as Mystical Fact (1902).
Approaching the Mystery of Golgotha (1914).
Autobiography: The Story of My Life (1928).
Free talking book versions available at rudolfsteineraudio.com.
Wills, Garry, What Jesus Meant (Viking Penguin: 2006).
What Paul Meant (Viking Penguin: 2007).
What the Gospels Meant (Viking Penguin: 2008).
Online resources:
https://biblehub.com/. Excellent website – particularly useful for checking comparative translations.
https://www.biblestudytools.com/. Excellent search engine. Very useful for checking such things as word usage frequency.
https://ccel.org/. Christian Classics Ethereal Library. Many free out-of-copyright resources. Impressive collection.
http://www.earlychristianwritings.com/. A very wide range of early Christian literature for free.
https://www.gutenberg.org/. Thousands of free out-of-copyright books. For instance, Albert Schweitzer’s The Quest of the Historical Jesus.
https://librivox.org Out-of-copyright talking books.
https://www.wikipedia.org/ A wonderful starting resource for any subject to do with Biblical studies.
You can also purchase university-level courses on Bible studies, Jewish history and Christian history from https://www.thegreatcourses.com/. These are done by top-level academics. Highly recommended.