Its meaning: The proverb “all work and no play makes Jack a dull boy” highlights the importance of activities of recreation, play, rest, leisure, etc. in our lives.
It means that if a person does too much mental tasks and is not able to find time for play, rest, and recreation, then finally his mind would turn dull and lazy. Slowly, he may start losing interest in his work.
Explanation: A man of flesh and blood cannot work always. He needs rest and recreation also. An office drudge becomes sick of daily grind. He feels relieved when he gets a holiday.
A student reads hard to pass an examination. When the examination is over, he gives up his studies and relaxes himself. A student minds his lessons during school hours, but he plays cricket or football in his free hours. However, he finds his studies dull and uninteresting, if he is asked to read without any play or recreation.
Work tires our body and mind. After a spell of hard work, we need some play or leisure. When we find some time to play, our health improves and the cheerfulness of our mind returns.
Constant pressure of work depresses our mind and impairs our health. So a boy becomes lovely and cheerful, when he has time to study and time to play. Work is always to be relieved by some form of play or recreation.