“Indeed, if you reach out to others, that is the main definition of humanity in a nutshell.”

Source: The Summing Up (1938), p. 206

Source: Going Postal

3 (20 October 1917); as published in The Blue Octavo Notebooks (1954); also in Dearest Father: Stories and Other Writings (1954); variant translations use "cardinal sins" instead of "main human sins" and "laziness" instead of "indolence".
The Zürau Aphorisms (1917 - 1918)
Context: There are two main human sins from which all the others derive: impatience and indolence. It was because of impatience that they were expelled from Paradise; it is because of indolence that they do not return. Yet perhaps there is only one major sin: impatience. Because of impatience they were expelled, because of impatience they do not return.

Source: Genome (1999), Chapter 10 “Stress” (p. 150)

Source: Magick Book IV : Liber ABA, Part III : Magick in Theory and Practice (1929), Ch. 1 : The Principles of Ritual
Context: There is a single main definition of the object of all magical Ritual. It is the uniting of the Microcosm with the Macrocosm. The Supreme and Complete Ritual is therefore the Invocation of the Holy Guardian Angel; or, in the language of Mysticism, Union with God.

2004 Christmas message http://news.bbc.co.uk/1/hi/uk/4125229.stm

Afro-Asian Conference (1965)
Context: For us there is no valid definition of socialism other than the abolition of the exploitation of one human being by another. As long as this has not been achieved, if we think we are in the stage of building socialism but instead of ending exploitation the work of suppressing it comes to a halt — or worse, is reversed — then we cannot even speak of building socialism.

Source: The Nature of Personal Reality (1974), p. 77: Session 617: September 25, 1972

Song lyrics, The Sensual World (1989)