“Love is the great test of the human. The human is tested by our ability to withstand love. Love is so difficult, it is so challenging, it demands of us that we wreck it with ourselves. It demands of us an honesty that few of us could sustain.”

"Love is a Battlefield" (co-written with Mike Chapman)

Lectures XIV and XV, "The Value of Saintliness"
1900s, The Varieties of Religious Experience (1902)
Context: The gods we stand by are the gods we need and can use, the gods whose demands on us are reinforcements of our demands on ourselves and on one another. What I then propose to do is, briefly stated, to test saintliness by common sense, to use human standards to help us decide how far the religious life commends itself as an ideal kind of human activity. … It is but the elimination of the humanly unfit, and the survival of the humanly fittest, applied to religious beliefs; and if we look at history candidly and without prejudice, we have to admit that no religion has ever in the long run established or proved itself in any other way. Religions have approved themselves; they have ministered to sundry vital needs which they found reigning. When they violated other needs too strongly, or when other faiths came which served the same needs better, the first religions were supplanted.

Remarks During Signing of Defense Bill http://www.washingtonpost.com/wp-dyn/articles/A42299-2004Aug5.html (5 August 2004).
2000s, 2004

The Bridge Across Forever (1984)
Source: The Bridge Across Forever: A True Love Story

On the famous statue "Juno Ludovisi", Letter 15
On the Aesthetic Education of Man (1794)

Letter Seven (14 May 1904)
Letters to a Young Poet (1934)
Variant: For one human being to love another human being: that is perhaps the most difficult task that has been given to us, the ultimate, the final problem and proof, the work for which all other work is merely preparation.
Source: The Selected Poetry of Rainer Maria Rilke
Context: People have (with the help of conventions) oriented all their solutions toward the easy and toward the easiest side of the easy; but it is clear that we must hold to what is difficult; everything alive holds to it, everything in Nature grows and defends itself in its own way and is characteristically and spontaneously itself, seeks at all costs to be so and against all opposition. We know little, but that we must hold to what is difficult is a certainty that will not forsake us; it is good to be solitary, for solitude is difficult; that something is difficult must be a reason the more for us to do it.
To love is good, too: love being difficult. For one human being to love another: that is perhaps the most difficult of all our tasks, the ultimate, the last test and proof, the work for which all other work is but preparation.

Rajagopalachari (12 February 1949), quoted in [Rajmohan Gandhi, Rajaji: A Life, http://books.google.com/books?id=JjPHeRd7_UYC&pg=PA475, 1997, Penguin Books India, 978-0-14-026967-3, 286]
Spoken by C.R when Mahatma Gandhi (Bapu) was assassinated.

Source: Simone Weil : An Anthology (1986), Love (1947), p. 270