To punish me for my contempt of authority, Fate has made me an authority myself.
为了惩罚我对权威的蔑视，命运使我本人成了权威。
Aphorism for a friend (18 September 1930) [Einstein Archive 36-598]; as quoted in Albert Einstein: Creator and Rebel (1988) by Banesh Hoffman (来源：www.EnglishCN.com)

The most incomprehensible thing about the world is that it is comprehensible.
这个世界最不可理解的事情在于它可以理解
"Physics and Reality" (1936) as quoted in Einstein: A Biography (1954) by Antonina Vallentin, p. 24.
Variants:

A happy man is too satisfied with the present to dwell too much on the future.

"My Future Plans" an essay written at age 17 for school exam (18 September 1896) The Collected Papers of Albert Einstein Vol. 1 (1987) Doc. 22

E = mc²
The equivalency of matter and energy was originally expressed by the equation m = L/c², which easily translates into the far more well known E = mc² in Does the Inertia of a Body Depend Upon Its Energy Content? published in the Annalen der Physik (27 September 1905) : "If a body gives off the energy L in the form of radiation, its mass diminishes by L/c²."

I am by heritage a Jew, by citizenship a Swiss, and by makeup a human being, and only a human being, without any special attachment to any state or national entity whatsoever.

Letter to Alfred Kneser (7 June 1918); Doc. 560 in The Collected Papers of Albert Einstein Vol. 8

How much do I love that noble man
More than I could tell with words
I fear though he'll remain alone
With a holy halo of his own.

Poem by Einstein on Spinoza (1920), as quoted in Einstein and Religion (1999) by Max Jammer "Einstein's Poem on Spinoza" (with scans of original German manuscript) at Leiden Institute of Physics, Leiden University

Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution.

"What Life Means to Einstein" in The Saturday Evening Post (26 October 1929)