4 He who has a slack hand becomes poor,
But the hand of the diligent makes rich.
5 He who gathers in summer is a wise son;
He who sleeps in harvest is a son who causes shame.
The online dictionary defines “slack” as: Verb 1. to neglect one's duty or work in a lazy manner and some synonyms are: idleness; carelessness; inefficiency; sloth.
This website also defines “diligent” as the exact opposite: Adjective 1. careful and persevering in carrying out tasks or duties 2. quietly and steadily persevering especially in detail or exactness
With these definitions, we can see that someone who is idle, careless and/or inefficient, and that neglects their work by doing it in a lazy manner WILL become poor for they will lose their jobs very quickly. The workers who are very careful to take care of all the details in their tasks or duties would quickly become valuable to their boss, and be promoted.
Verse 5 speaks of those who “gather” in the season for gathering in a harvest (summer). When they do the work, when it needs to be done, then they are being wise, while those that are lazy and don’t take advantage of the “window” when the harvest is ready, will end up with little or nothing to show and this will bring shame to them.