In this broad earth of ours,
Amid the measureless grossness and the slag,
Enclosed and safe within its central heart,
Nestles the seed perfection. ~ Walt Whitman
Thou shalt be perfect with the Lord thy God. ~ Deuteronomy
Misato: So fucking what if I’m not you?! That doesn’t mean its okay for you to give up! If you do, I’ll never forgive you as long as I live. God knows I’m not perfect either. I’ve made tons of stupid mistakes and later I regretted them. And I’ve done it over and over again, thousands of times. A cycle of hollow joy and vicious self-hatred. But even so, every time I learned something about myself. Please, Shinji. You’ve got to pilot Eva and settle this once and for all. For your own sake. Find out why you came here. Why you exist at all. Answer your own questions. And when you’ve found your answers, come back to me. I’ll be waiting for you. Promise me.
That is the true perfection of man to find out his imperfections.
Augustine of Hippo, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 449.
Perfect water - the dark wind braids the waves.
The crazed birds raid the trees. is this our destiny?
To join our hands at sea - and slowly sink, and slowly think:
This is perfect water, passing over me.
We should not insist on absolute perfection of the gospel in our fellow Christians, however we may strive for it ourselves.
John CalvinGolden Booklet of the True Christian Life, pg. 21
This is the highest honour of the Church, that, until He is united to us, the Son of God reckons himself in some measure imperfect. What consolation is it for us to learn, that, not until we are along with him, does he possess all his parts, or wish to be regarded as complete! Hence, in the First Epistle to the Corinthians, when the apostle discusses largely the metaphor of a human body, he includes under the single name of Christ the whole Church.
Commentary on Ephesians 1:23.
John CalvinCommentaries on the Epistles of Paul to the Galatians and Ephesians, 1854, Rev. William Pringle, tr., Edinburgh, p. 218. 
Perfection is the dream of imperfection that refuses to wake up.
Fausto Cercignani in: Brian Morris, Quotes we cherish. Quotations from Fausto Cercignani, 2013, p. 19.
There is but one true good for a spiritual being, and this is found in its perfection. Men are slow to see this truth; and yet it is the key to God's providence, and to the mysteries of life.
William Ellery Channing, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 449.
It seems like the better it gets, the more miserable people become. There’s never a technological advancement where people think, “Wow, we can finally do this!” … And I think a lot of it has to do with advertising. Americans have it constantly drilled into our heads, every fucking day, that we deserve everything to be perfect all the time.
"Only he is the true teacher [Satguru] who can show what are the religious and social obligations [dharma], show God to you, and give you the Knowledge of the holy name [sat nam]. And he who can give you the Knowledge of this dharma is completely wise. Satguru is the one who has the perfect wisdom. And other than the Satguru no one has the perfect wisdom. Oh! People of the world! Only a perfect avatar with the sixty-four virtues [kala] can reveal this Knowledge." (Bombay, March 1966) 
Alternative translation: "Lord Rama was an incarnation of God who possessed 14 types of divine power. Lord Krishna was an incarnation of God who possessed 26 types of divine power. But I am fully perfect and the master of all the 64 divine powers."
This alternative translation, very different from the original Hindi, appeared in a book named Satgurudev (1970). It has been used by several scholars (Messer, Glock and Bellah; Reender Kranenborg) to position Hans Ji Maharaj as claiming to be more powerful than Krishna.
Those who aim at faultless regularity will only produce mediocrity, and no one ever approaches perfection except by stealth, and unknown to themselves.
William Hazlitt, "Thoughts on Taste", The Edinburgh Magazine, July 1819, final paragraph.
Kevin Flynn: The thing about perfection is that it's unknowable. It's impossible, but it's also right in front of us, all the time. You wouldn't know that because I didn't, when I created you...I'm sorry, CLU...I'm sorry.
Kevin Flynn (played by Jeff Bridges), Tron Legacy, story by Adam Horowitz and Edward Kitsis
Immaculate being... Was it? In this secular existence, perfection is an illusion, regardless of those who utter the contrary. This is the reality. Common man seeks it out, they strive to achieve it, as if it were some tangible thing... But... The fact of the matter is, perfection is a hollow shell. It is devoid of any substance. I spit on perfection. Perfection, after all, implies you've reached the summit. No trial and error, no ability to conceptualize. An omniscient being would have no need for such superfluous things... Am I making myself clear? For people who dabble in the sciences, such as ourselves, perfection would make us obsolete. Many magnificent things have been, and will continue to come into existence... And yet, every last one of them will fall short of perfection's finish. Our function as men of science relies on their many shortcomings. Then, and only then, can we apply the fruits of our labor. To put it simply... As soon as you began spouting that nonsense about perfection, your fate was sealed. You dare call yourself a man of science?
We are morally and intellectually superior to all men. We are peerless. So, too, are our organizations and our institutions. [Germany was] the most perfect political creation known to history, [the Kaiser] deliciae humani generis, [and the Imperial Chancellor, Herr von Bethmann-Hollweg] the most eminent of living men.
Adolf Lasson; The Times (London), History of the War (1915), vol. 5, p. 170. This noted Hegelian philosopher and German nationalist is also quoted by Georges Clemenceau, Grandeur and Misery of Victory, p. 278 (1930).
Drummond: All shine, and no substance! Bert, whenever you see something bright, shining, perfect-seeming—all gold, with purple spots—look behind the paint! And if it’s a lie—show it up for what it really is!
Whoever has received from the divine bounty a large share of temporal blessings, whether they be external and material, or gifts of the mind, has received them for the purpose of using them for the perfecting of his own nature, and, at the same time, that he may employ them, as the steward of God's providence, for the benefit of others.
It is a union with a Higher Good by love, that alone is endless perfection. The only sufficient object for man must be something that adds to and perfects his nature, to which he must be united in love; somewhat higher than himself, yea, the highest of all, the Father of spirits. That alone completes a spirit and blesses it, — to love Him, the spring of spirits.
Robert Leighton, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 449.
Kirk: I am the Kirk, the creator?
Nomad: You are the creator.
Kirk: You're wrong! Jackson Roykirk, your creator, is dead. You have mistaken me for him. You are in error! You did not discovered your mistake; you have made two errors. You are flawed and imperfect, and you have not corrected by sterilization; you're made three errors!
Nomad': Error? Error? Error? Examine.
Star Trek: The Original Series]] The Changeling John Meredyth Lucas
The essence of being human is that one does not seek perfection, that one is sometimes willing to commit sins for the sake of loyalty, that one does not push asceticism to the point where it makes friendly intercourse impossible, and that one is prepared in the end to be defeated and broken up by life, which is the inevitable price of fastening one's love upon other human individuals.
A totalitarian state is in effect a theocracy, and its ruling caste, in order to keep its position, has to be thought of as infallible. But since, in practice, no one is infallible, it is frequently necessary to rearrange past events in order to show that this or that mistake was not made, or that this or that imaginary triumph actually happened. Then, again, every major change in policy demands a corresponding change of doctrine and a revaluation of prominent historical figures.
Are you not ashamed that you give your attention to acquiring as much money as possible, and similarly with reputation and honor, and give no attention or thought to truth and understanding and the perfection of your soul?
"Perfect the Will, the Mind, Feeling, their corporeal organs and their material tools; be useful to yourselves, to your own ones, and to others; and Happiness, insofar as it exists on this earth, will come of itself."
You will remember that Christ said, "Judge not lest ye be judged." That principle I do not think you would find was popular in the law courts of Christian countries. I have known in my time quite a number of judges who were very earnest Christians, and none of them felt that they were acting contrary to Christian principles in what they did. Then Christ says, "Give to him that asketh of thee, and from him that would borrow of thee turn not thou away." That is a very good principle... Then there is one other maxim of Christ which I think has a great deal in it, but I do not find that it is very popular among some of our Christian friends. He says, "If thou wilt be perfect, go and sell that which thou hast, and give to the poor." That is a very excellent maxim, but, as I say, it is not much practised. All these, I think, are good maxims, although they are a little difficult to live up to. I do not profess to live up to them myself; but then, after all, it is not quite the same thing as for a Christian.
I think the destiny of all men is not to sit in the rubble of their own making but to reach out for an ultimate perfection which is to be had. At the moment, it is a dream. But as of the moment we clasp hands with our neighbor, we build the first span to bridge the gap between the young and the old. At this hour, it’s a wish. But we have it within our power to make it a reality. If you want to prove that God is not dead, first prove that man is alive.
No one can be perfectly free till all are free; no one can be perfectly moral till all are moral; no one can be perfectly happy till all are happy.
Herbert Spencer, Social Statics (1851), part 4, chapter 30, last sentence, p. 456.
We are all imperfect. We can not expect perfect government.
William Howard Taft, address at a banquet given in his honor by the Board of Trade and Chamber of Commerce of Washington, D.C. (May 8, 1909); Presidential Addresses and State Papers of William Howard Taft (1910), vol. 1, chapter 7, p. 82.
Perfectly beautiful: let it be granted her: where is the fault?
All that I saw (for her eyes were downcast, not to be seen)
Faultily faultless, icily regular, splendidly null, Dead perfection, no more.
Voltaire credits the Italian origin, ascribing it to an unnamed "Italian sage" or "wise Italian":
Dans ses écrits un sage Italien
Dit que le mieux est l'ennemi du bien.
In his writings a wise Italian
Says that the better is the enemy of the good.
He also gives the saying (without attribution) in Italian (Il meglio è l'inimico del bene [note spelling difference: l'inimico instead of nemico for "[the] enemy") in the article "Art Dramatique" ("Dramatic Art", 1770) in the Dictionnaire philosophique.
Aristotle especially, both by speculation and observation... reached something like the modern idea of a succession of higher organizations from lower, and made the fruitful suggestion of "a perfecting principle" in Nature. With the coming in of Christian theology this tendency toward a yet truer theory of evolution was mainly stopped, but the old crude view remained...
Math is perfect (in principle), but mathematicians are not (because they are humans), hence the mathematics that (human) mathematicians do is influenced by the weltanschauung of the people around them.
Doron Zeilberger "Computerized Deconstruction". Appeared in Adv. Appl. Math. v. 31 (2003), 532-543.