It means to be diligent in thinking, agile in action, strong in ability and careful in speaking. In other words, do more and think less.

Source:

The Analects of Confucius in the Spring and Autumn Period: "A gentleman wants to speak slowly but act quickly."

Translation:

Confucius said, "A gentleman speaks slowly with caution, but acts quickly.

Extended data:

People's ability to do things and language skills are often out of proportion. What you can say may not be done, and what you can do may not be said. It is rare to see people who both do well and speak beautifully. We have discussed the advantages and disadvantages of eloquent people, and put forward that eloquent people must "listen to what they say and observe what they do".

If you speak carefully, you won't shut up. You won't leave any room for yourself. Speak appropriately, talk less nonsense and rhetoric, but don't be too careful not to speak. Agility means that you must make a quick commitment to what you have said. Don't just play with words, do more practical things.

References:

Baidu Encyclopedia-The Analects of Confucius Liren