The belief that all mystical experiences are “ultimately one,” and thus somehow in essence are “the same” is a common modern claim, which requires some reflective analysis. It is generally made by two groups. First Neomystics generally posit a transcendental unity of religion and God, and believe that God/the Ultimate manifests him/her/itself in different ways and with different symbols to different cultures in different times. But at root, all these are culturally-based manifestations of the same transcendent God. (This belief, by the way, ultimately derives from syncretism Vedantic Hindu pantheistic assumptions.) The second group are secularists, who agree that all mystical experiences are at root the same because they are entirely internal mental phenomena caused by human brain chemistry. There is no outside reality causing the mystical experience. It is only (aberrant?) brain chemistry that humans wrongly believe to be caused by an external force of some kind. These two groups thus share this universalist mystical claim, though for drastically different reasons.
Our knowledge of the nature and meaning of mystical experiences drives from two sources: 1- personal mystical experience, and 2- reports of the mystical experiences of others. However, mystics almost universally claim that mystical experiences are ineffable. They cannot be explained to others. They cannot be learned from others. They must be experienced first hand to be understood. Thus, studying reports of the mystical experiences of others is an inadequate means of understanding the reality of mystical experiences. The mystics themselves insist upon this. As Laozi, one of the great Chinese mystics, said: zhī zhě bù yàn; yàn zhě bù zhī. (“He who knows does not speak; he who speaks does not know.”) What mystics report–and can only report–is an inadequate symbolic, allegorical model of what they experience. But map is not territory. Looking at a map of Tibet is nowhere near the experience of visiting Tibet. It lets you know there is a place called Tibet, and it will help you know how to get there, but it is not visiting Tibet.
Now, from a practical and objective point of view, what mystics report of their actual mystical experiences are often dramatically, even drastically different. Yes, many mystics report that they feel an intense, overwhelming bliss and joy, and a oneness with God. But no Buddhist or Hindu mystic ever reports seeing the Virgin Mary crowned with twelve stars (Rev. 12:1). No medieval Christian mystic ever reports having oneness with the divine while have ritual physical sex like Tantric Hindu mystics might. No traditional Jewish mystic is ever tempted by the demon Mara like Tibetan mystics are. Without a pre-existing assumption that all mystical experiences are somehow one, no one reading the actual reports of the vastly different mystical experiences from many different cultures and times would possibly assume they are describing the same thing. The reports are, in fact, extraordinarily diverse.
Thus, the claim that all mystical experiences are the same is in fact an esoteric interpretation of the “real” meaning of mystical experiences, which are themselves esoteric descriptions of spiritual phenomena. It is further esotericizing the already esoteric. In fact, it represents a devaluation of the authenticity of the mystical claims of traditional mystics. A Muslim, Christian, or Jewish mystic believes that their mystical experience represents an authentic encounter with God. The Neomystics (along with the secularists), on the other hand, claim that the traditional mystics have fundamentally misunderstood their own mystical experience. A traditional Christian mystic might claim she actually saw the real Virgin Mary. The universalistic claim of the Neomystics implies that the vision of the Virgin Mary is not an authentic encounter with God in and of itself, but is a cultural-based symbol, which is in fact a further barrier to the real authentic encounter with the transcendental God beyond and behind the symbols of all traditional mystical experiences. In reality, the claim that all mystical experiences are ultimately the same is a culturally-based belief just as much as the claim that a medieval Christian mystic saw the Virgin Mary. It is not the reconciliation, transcending and uniting of all mystical experiences. It is, in fact, a new culturally based (mis-?) understanding of traditional mystical experiences, which necessarily devalues those traditional mystical experiences. It is a new form mysticism, which, while claiming to unite all others, in fact creates a new, different mystical system.