“Guard well your spare moments. They are like uncut diamonds. Discard them and their value will never be known. Improve them and they will become the brightest gems in a useful life.”

Literary Journals.
Curiosities of Literature (1791–1834)

Isaac D'Israeli, The Curiosities of Literature, "Literary Journals".
Misattributed, Isaac D'Israeli

New England Weather, speech to the New England Society (December 22, 1876)

Leaves Of Morya's Garden (1924 - 1925), Book I : The Call (1924)
Context: By holiness in life, guard the precious Gem of Gems.
Aum Tat Sat Aum!
I am thou, thou art I — parts of the Divine Self.
My Warriors! Life thunders — be watchful.
Danger! The soul hearkens to its warning!
The world is in turmoil — strive for salvation.
I invoke blessings unto you.
Salvation will be yours!
Life nourishes the soul.
Strive for the life glorified,
and for the realization of purity.
Put aside all prejudices — think freely.
Be not downcast but full of hope.
Flee not from life, but walk the path of salvation.

Quote in a letter to Umberto Boccioni, 1910; as cited in Gino Severini, the Dance, 1909 – 1916, by Daniele Fonti, Peggy Guggenheim Collection, Venice; 2001, p. 15

Book I, Ch. 20
Attributed

Sakhi, 170; translation by Yashwant K. Malaiya based on that of Puran Sahib.
Bijak

Lilith, in Pt. V
1920s, Back to Methuselah (1921)
Context: I say, let them dread, of all things, stagnation; for from the moment I, Lilith, lose hope and faith in them, they are doomed. In that hope and faith I have let them live for a moment; and in that moment I have spared them many times. But mightier creatures than they have killed hope and faith, and perished from the earth; and I may not spare them for ever. I am Lilith: I brought life into the whirlpool of force, and compelled my enemy, Matter, to obey a living soul. But in enslaving Life's enemy I made him Life's master; for that is the end of all slavery; and now I shall see the slave set free and the enemy reconciled, the whirlpool become all life and no matter. And because these infants that call themselves ancients are reaching out towards that, I will have patience with them still; though I know well that when they attain it they shall become one with me and supersede me, and Lilith will be only a legend and a lay that has lost its meaning. Of Life only is there no end; and though of its million starry mansions many are empty and many still unbuilt, and though its vast domain is as yet unbearably desert, my seed shall one day fill it and master its matter to its uttermost confines. And for what may be beyond, the eyesight of Lilith is too short. It is enough that there is a beyond.

Georges Duhamel in THE HEART'S DOMAIN (1919). As it was composed in French, the wording in English may vary in translation. Theodore Geisel / Dr. Seuss was born in 1904, and would have been about 15 years old at the time that it was published. The full text can be found at the link below: We do not know the true value of our moments until they have undergone the test of memory. Like the images the photographer plunges into a golden bath, our sentiments take on color; and only then, after that recoil and that trans-figuration, do we understand their real meaning and enjoy them in all their tranquil splendor.
Misattributed