By “sin” must be understood our separation from the Divine Center insofar as this shows itself in attitudes or acts; the essence of sin is a forgetting of the Absolute, which is at the same time the Infinite and the Perfect, and this forgetting coincides with centrifugal passion and at the same time with egoistic hardening. [GTUFS: TransfMan, Usurpations of Religious Feeling]

If we wish to give the word “sin” its broadest or deepest meaning, we would say that it expresses above all an attitude of the heart; hence a “being” and not a simple “doing” or “not doing” . . . According to the Bible  , the forbidden tree was that of the discernment between “good” and “evil”; now this discernment, or this difference, pertains to the very nature of Being; consequently, its source could not be in the creature; to claim it for oneself is to wish to be equal to the Creator, and that is the very essence of sin; of all sin. Indeed, the sinner decides what is good, counter to the objective nature of things; he willingly deludes himself about things and about himself, whence the fall, which is nothing other than the reaction of reality. [GTUFS: PlayMasks, Delineations of Original Sin]

“Sin” is thus defined as an act which, firstly, is opposed to the divine Nature in one or another of its forms or modes (the reference here is to the Divine Qualities and the intrinsic virtues which reflect them) and which, secondly, engenders in principle posthumous suffering; it does so “in principle”, but not always in fact, for repentance and positive acts on the one hand and the divine Mercy on the other efface sins, or can efface them. [GTUFS: LightAW, In the Wake of the Fall]

Sin (by omission): According to the Apostle James, he who knows to do good and does not do it, commits a sin; this is the very definition of sin by omission, but at the same time it goes beyond the framework of a formalistic and exoteric morality. [GTUFS: PlayMasks, Delineations of Original Sin]