from The Analects of Confucius (Kongfuzi), 4:15, on the "one thread," or yi guan:

Confucius said, "Shen, there is one thread that runs through my doctrines."
He replied, "Yes."
After Confucius had left, the disciples asked him, "What did he mean?"
He replied, "The Way of our Master is none other than conscientiousness (chung) and altruism (shu)."

As explained in the commentary of Wing-Tsit Chan (whose translation I'm playing off here):

Confucian teachings may be sumed up in the phrase "one thread" (i-kuan), but Confucianists have not agreed on what it means....
All agree, however on the meanings of chung and shu, which are best expressed by Chu Hsi, namely, chung means the full development of one's [originally good] mind and shu means the extension of that mind to others. As Ch'eng I put it, chung is the Way of Heaven, whereas shu is the way of man; the former is substance, while the latter is function....
Here is the positive version of the Confucian golden rule.

Guan, meaning "thread on a loom," is also pun on the Mandarin words for "government official," "smiling," and "coffin," all of which are probably important. Kongfuzi was a bit of a joker that way. But mostly, this would be about the weaving together of conscientiousness and altruism -- thoughtfulness and good deeds.

There's a really nice introduction to Confucius put up by the Friesians, which translates chung (or zhong) as "loyalty" and shu as "reciprocity." But it also has diagrams and stuff. Highly recommended for chart-lovers like me.