The word “esoterism” suggests in the first place an idea of complementarity, of a “half” as it were: esoterism is the complement of exoterism, it is the “spirit” which completes the “letter”. Where there is a truth of Revelation, hence of formal and theological truth, there must also be a truth of intellection, hence of non-formal and metaphysical truth; not legalistic or obligatory truth, but truth that stems from the nature of things, and which is also vocational since not every man grasps this nature. But in fact this second truth exists independently of the first; hence it is not, in its intrinsic reality, a complement or a half; it is so only extrinsically and as it were “accidentally”. This means that the word “esoterism” designates not only the total truth inasmuch as it is “colored” by entering a system of partial truth, but also the total truth as such, which is colorless. This distinction is not a mere theoretical luxury; on the contrary, it implies extremely important consequences. Thus esoterism as such is metaphysics, to which is necessarily joined an appropriate method of realization. But the esoterism of a particular religion – of a particular exoterism precisely – tends to adapt itself to this religion and thereby enter into theological, psychological and legalistic meanders foreign to its nature, while preserving in its secret center its authentic and plenary nature, but for which it would not be what it is. [GTUFS: SurveyME, Two Esoterisms]
Esoterism it is that lays bare either the relativity of an apparent absoluteness or the absoluteness of an apparent relativity. Seen from high above, the absolutism of a given form reveals its limits, while the existential contingency of a given phenomenon reveals, on the contrary, its essential absoluteness, so that one and the same sacred element, after having lost the formally absolute character attributed to it by the exoteric perspective, assumes so to speak another absoluteness, or rather reveals it, namely that of the archetype which it manifests. The Gospel   appears absolute inasmuch as it imposes itself on Christians as the unique word of God; but the esoteric vision of things enables us, on the one hand, to discover the limits of this totalitarianism, and, on the other, to discern in this very Gospel the absoluteness of the Divine Word as such, the Word from which all Revelations derive. [GTUFS: LogicT, The Problem of Qualifications]
Esoterism is so to speak the “religion of intelligence”: this means that it operates with the intellect – and not with sentiment and will only – and that consequently its content is all that intelligence can attain, and that it alone can attain.* The “subject” of esoterism is the Intellect and its “object” is ipso facto total Truth, namely – expressed in Vedantic terms – the doctrine of Atma and Maya; and he who says Atma and Maya thereby says Jnana, direct knowledge, intellectual intuition. (*It is far from being the case that all historical esoterism is esoterism pure and simple; an exegesis colored by confessional bias, or overly involved in mystical subjectivism is far from true gnosis. On the other hand, it is far from being the case that all that is put into the category of esoterism pertains to it: it too often happens that in treating this subject authors make no distinction between what is genuine and what is counterfeit, thus between truth and error, in accordance with the two sins of our time which are the replacement of intelligence by psychology and confusion between the psychic and the spiritual.) [GTUFS: HaveCenter, Intelligence and Character]
If one may define esoterism as a “shortcut” not within reach of every mental make-up or every degree of intellectual scope, the Adamantine Vehicle, with its perspective of “ubiquity” and its quasi-theurgic method of mantra, provides a particularly conclusive example of what constitutes an esoteric method. [GTUFS: TreasuresB, Message and Messenger]

Esoterism (authentic): Authentic esoterism stems from the nature of things and not from a dynastic institution; its seeds are everywhere present, sparks can flash from every flint; to make esoterism result from a religious program and a theological argument is a contradiction in terms. [GTUFS: FaceA, Diversity of Paths]
Authentic esoterism – let us say it again – is the way which is founded on total or essential truth, and not merely on partial or formal truth, and which makes an operative use of the intelligence, and not only of the will and the feelings. The totality of truth demands the totality of man. [GTUFS: SufismVQ, Human Premises of a Religious Dilemma]

Esoterism / Apostasy: Esoterism, which brings limitations back to their unlimited archetypes, and apostasy, which rids itself of them in favor of nothingness. [GTUFS: ChristIslam, The Idea of “The Best” in Religions]
Esoterism / Ascesis: The apparently problematical – but in reality elliptical – equation “esoterism equals ascesis” means in substance: esoterism is the elimination of the individual obstacles which prevent or “veil” the irradiation of the divine Self in the soul . . . the removal of an obstacle in view of the “unveiling” of the one Reality. [GTUFS: SurveyME, Enigma and Message of Islamic Esoterism]

Esoterism / Gnosis: Direct and inward knowledge, that of the Heart-Intellect, is what the Greeks called gnosis; the word “esoterism” – according to its etymology – signifies gnosis inasmuch as it de facto underlies the religious, and thus dogmatic doctrines. [GTUFS: EsoterismPW, Understanding Esoterism]