Mencius, known as Meng Ke, was a renowned thinker of the Warring States period who, like Confucius, taught many disciples.
Once, a student asked him, "Master, there are so many things to do and learn now. What should I know first and do first?"
Mencius replied, "A wise sage knows everything they need to know, but they prioritize what is most urgent. Though they love all people, they first love their own family and the worthy. Even the ancient sages Yao and Shun, who were all-knowing, understood this—they focused on what mattered most and first cherished their kin and the virtuous."
Next, Mencius used a counterexample to illustrate his point:
For example, if a person's parents die, custom requires a three-year mourning period. But if he skips the three years yet fusses over minor rituals of three or five months, he has missed what truly matters. Similarly, if someone gulps soup noisily and chews loudly at an elder's table, yet lectures about not tearing dried meat with his teeth, he is neglecting the essential for the trivial—utterly failing to grasp his real priorities.
The student nodded and said, "Teacher, I understand." Later, the idiom "the most urgent matter" came to describe the most pressing task among current priorities.
Source: *Mencius*, Chapter "Jin Xin"
Meaning of the Idiom: Later, the Chinese idiom "当务之急" came to describe the most pressing task among current priorities.