“This spiritual freedom, the opposite of insensitivity or laziness, freedom to suffer and to know error, is the nearness and very redemption of God.”

Volume 1, p. 191
The Prophets (1962)

The Hindu Way ( Page 55 )

Redemption Song
Uprising (1979)

Freedom: Foster It! p. 114.
Freedom: Foster it! (2004)

Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter LXXVII: On Taking One’s Own Life

King quoted here John F. Kennedy who at the signing of a charter establishing the German Peace Corps in Bonn, West Germany (24 June 1963) remarked: Dante once said that the hottest places in hell are reserved for those who, in a period of moral crisis, maintain their neutrality.
According to Bartleby.com, Kennedy's remark may have been inspired by the passage from Dante Alighieri’s La Comedia Divina “Inferno,” canto 3, lines 35–42 (1972) passage as translated by Geoffrey L. Bickersteth: "by those disbodied wretches who were loth when living, to be either blamed or praised. [...] Fear to lose beauty caused the heavens to expel these caitiffs; nor, lest to the damned they theng ave cause to boast, receives them the deep hell." A more modern-sounding translation from the foregoing Dante’s Inferno passage was translataed 1971 by Mark Musa thus: “They are mixed with that repulsive choir of angels … undecided in neutrality. Heaven, to keep its beauty, cast them out, but even Hell itself would not receive them for fear the wicked there might glory over them.”
This is also often quoted slightly differently as: "The hottest place in Hell is reserved for those who remain neutral in times of great moral conflict"
1960s, Why I Am Opposed to the War in Vietnam (1967)
Context: I see this war as an unjust, evil, and futile war. I preach to you today on the war in Vietnam because my conscience leaves me with no other choice. The time has come for America to hear the truth about this tragic war. In international conflicts, the truth is hard to come by because most nations are deceived about themselves. Rationalizations and the incessant search for scapegoats are the psychological cataracts that blind us to our sins. But the day has passed for superficial patriotism. He who lives with untruth lives in spiritual slavery. Freedom is still the bonus we receive for knowing the truth. "Ye shall know the truth," says Jesus, "and the truth shall set you free." Now, I've chosen to preach about the war in Vietnam because I agree with Dante, that the hottest places in hell are reserved for those who in a period of moral crisis maintain their neutrality. There comes a time when silence becomes betrayal.

Old Path White Clouds : Walking in the Footsteps of the Buddha (1991) Parallax Press ISBN 81-216-0675-6

No Antithesis indicated.
Gesammelte Mathematische Werke (1876)

Apostolic Letter, Salvifici Doloris (“redemptive suffering”), 1984
Source: http://w2.vatican.va/content/john-paul-ii/en/apost_letters/1984/documents/hf_jp-ii_apl_11021984_salvifici-doloris.html