“The true clerc is Vauvenargues, Lamarck, Fresnel, … Spinoza, Schiller, Baudelaire, César Franck, who were never diverted from single-hearted adoration of the beautiful and the divine by the necessity of earning their daily bread. But such clercs are inevitably rare. … The rule is that the living creature condemned to struggle for life turns to practical passions, and thence to the sanctifying of those passions.”

Source: Treason of the Intellectuals (1927), p. 158

Ein Mensch wie ich kann ohne Steckenpferd, ohne herrschende Leidenschaften, ohne einen Tyrannen in Schillers Worten, nicht leben. Ich habe meinen Tyrannen gefunden und in seinem Dienst kenne ich kein Maß.
Letter to Wilhelm Fliess (1895), as quoted in Journal of the History of the Behavioral Sciences Vol 3-4 (1967) p. 159
1890s
Context: A man like me cannot live without a hobby-horse, a consuming passion — in Schiller's words a tyrant. I have found my tyrant, and in his service I know no limits. My tyrant is psychology. it has always been my distant, beckoning goal and now since I have hit upon the neuroses, it has come so much the nearer.

Vol. 1: 'My beautiful One, My Unique!', pp. 130-140
1895 - 1905, Lettres à un Inconnu, 1901 – 1905; Museo Communale, Ascona

Source: Discipleship (1937), Revenge, p. 142.
Context: The passion of Christ is the victory of divine love over the powers of evil, and therefore it is the only supportable basis for Christian obedience. Once again, Jesus calls those who follow him to share his passion. How can we convince the world by our preaching of the passion when we shrink from that passion in our own lives? On the cross Jesus fulfilled the law he himself established and thus graciously keeps his disciples in the fellowship of his suffering.

Quoted in Monteux, Doris G (1965). It's All in the Music: The Life and Work of Pierre Monteux. New York: Farrar, Straus and Giroux. OCLC 604146, p. 196

Source: Intuitions and Summaries of Thought (1862), Volume I, p. 240.