“The philosopher says that God's knowledge is the measure of things, and that things are the measure of man's knowledge.”

As quoted in Theaetetus by Plato section 152a

ibid.

§ I
1910s, At the Feet of the Master (1911)
Context: In all the world there are only two kinds of people — those who know, and those who do not know; and this knowledge is the thing which matters. What religion a man holds, to what race he belongs — these things are not important; the really important thing is this knowledge — the knowledge of God's plan for men. For God has a plan, and that plan is evolution. When once a man has seen that and really knows it, he cannot help working for it and making himself one with it, because it is so glorious, so beautiful. So, because he knows, he is on God's side, standing for good and resisting evil, working for evolution and not for selfishness.
If he is on God's side he is one of us, and it does not matter in the least whether he calls himself a Hindu or a Buddhist, a Christian or a Muhammadan, whether he is an Indian or an Englishman, a Chinaman or a Russian. Those who are on His side know why they are here and what they should do, and they are trying to do it; all the others do not yet know what they should do, and so they often act foolishly, and try to invent ways for themselves which they think will be pleasant for themselves, not understanding that all are one, and that therefore only what the One wills can ever be really pleasant for any one. They are following the unreal instead of the real. Until they learn to distinguish between these two, they have not ranged themselves on God's side, and so this discrimination is the first step.
But even when the choice is made, you must still remember that of the real and the unreal there are many varieties; and discrimination must still be made between the right and the wrong, the important and the unimportant, the useful and the useless, the true and the false, the selfish and the unselfish.

Source: Disturbing the Peace (1986), Ch. 1 : Growing Up "Outside", p. 13
Context: The most important thing is that man should be the measure of all structures, including economic structures, and not that man be made to measure for those structures. The most important thing is not to lose sight of personal relationships — i. e., the relationships between man and his co-workers, between subordinates and their superiors, between man and his work, between this work and its consequences.

Book 1 Chapter 1, p. 44
Institutes of the Christian Religion (1536; 1559)
Context: Without knowledge of self there is no knowledge of God.
Our wisdom, in so far as it ought to be deemed true and solid Wisdom, consists almost entirely of two parts: the knowledge of God and of ourselves. But as these are connected together by many ties, it is not easy to determine which of the two precedes and gives birth to the other.

page 85
Fooled by Randomness (2001)

Introduction<!-- p. 1-2 -->
Space—Time—Matter (1952)
Context: The Greeks made Space the subject-matter of a science of supreme simplicity and certainty. and certainty Out of it grew, in the mind of classical antiquity, the idea of pure science. Geometry became one of the most powerful expressions of that sovereignty of the intellect that inspired the thought of those times. At a later epoch, when the intellectual despotism of the Church... had crumbled, and a wave of scepticism threatened to sweep away all that had seemed most fixed, those who believed in Truth clung to Geometry as to a rock, and it was the highest ideal of every scientist to carry on his science "more geometrico". Matter... could be measured as a quantity and... its characteristic expression as a substance was the Law of Conservation of Matter... This, which has hitherto represented our knowledge of space and matter, and which was in many quarters claimed by philosophers as a priori knowledge, absolutely general and necessary, stands to-day a tottering structure.

Two Precepts of Charity (1273)
Sermons on the Ten Commandments (Collationes in decem praeceptes, c. 1273), Prologue (opening sentence)
Variant translation: Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do.
Original: (la) Tria sunt homini necessaria ad salutem: scilicit scientia credendorum, scientia desiderandorum, et scientia operandorum.

On Contradiction (1937)
Original: (zh-CN) 就人类认识运动的秩序说来，总是由认识个别的和特殊的事物，逐步地扩大到认识一般的事物。人们总是首先认识了许多不同事物的特殊的本质，然后才有可能更进一步地进行概括工作，认识诸种事物的共同的本质。